Samacheer Kalvi Class 6 Science Solutions Term 2 Chapter 4 Air

Samacheer Kalvi 6th Science Air Text Book Back Questions and Answers

I. Choose the Correct Answer:

 

Question 1. ........ is the percentage of nitrogen in the air.
(a) 78%
(b) 21%
(c) 0.03%
(d) 1%
Answer: (a) 78%
In simple words: Nitrogen makes up the biggest part of the air we breathe. It is about 78% of all the air around us.

🎯 Exam Tip: Remember the approximate percentages of the main gases in the atmosphere (nitrogen, oxygen, argon, carbon dioxide) for quick recall in MCQs.

 

Question 2. Gas exchange takes place in plants using ........
(a) Stomata
(b) Chlorophyll
(c) Leaves
(d) Flowers
Answer: (a) Stomata
In simple words: Plants breathe through tiny holes on their leaves called stomata. These holes open and close to let gases like carbon dioxide and oxygen in and out.

🎯 Exam Tip: Stomata are crucial for both photosynthesis (taking in CO2) and respiration (releasing CO2 and taking in O2) in plants.

 

Question 3. The constituent of air that supports combustion is ........
(a) Nitrogen
(b) carbon-di-oxide
(c) Oxygen
(d) water vapour
Answer: (c) Oxygen
In simple words: For anything to burn, it needs oxygen. Oxygen helps keep a fire going, so it is a supporter of combustion.

🎯 Exam Tip: Always associate oxygen with burning or combustion, as it is the key gas that allows these reactions to occur.

 

Question 4. Nitrogen is used in the food packaging industry because it ........
(a) provides colour to the food
(b) provides oxygen to the food
(c) adds proteins and minerals to the food
(d) keeps the food fresh
Answer: (d) keeps the food fresh
In simple words: Nitrogen gas is used in food packets to stop food from going bad quickly. It prevents unwanted chemical reactions that spoil the food.

🎯 Exam Tip: Nitrogen is an inert gas, meaning it does not react easily, which makes it perfect for keeping packaged foods fresh by displacing oxygen.

 

Question 5. ........ and ........ are the two gases, which when taken together, make up about 99 percentage of air.
I. Nitrogen
II. carbon-di-oxide
III. Noble gases
IV. Oxygen
(a) I and II
(b) I and III
(c) II and IV
(d) I and IV
Answer: (d) I and IV
In simple words: Nitrogen and oxygen are the two main gases that make up almost all of the air we breathe. Together, they form about 99% of the atmosphere.

🎯 Exam Tip: Nitrogen makes up about 78% of air, and oxygen about 21%, adding up to roughly 99% of the total atmospheric composition.

II. Fill in the Blanks

 

Question 1. ........ is the active component of air.
Answer: Oxygen \( (\text{O}_2) \).
In simple words: Oxygen is the most active part of the air. It is very important for living things to breathe and for things to burn.

🎯 Exam Tip: An "active component" means the part that readily reacts with other substances, which oxygen does, supporting life and combustion.

 

Question 2. The gas given out during photosynthesis is ........
Answer: Oxygen \( (\text{O}_2) \).
In simple words: Plants make oxygen when they do photosynthesis. They release this oxygen into the air for us to breathe.

🎯 Exam Tip: Photosynthesis is the process by which plants use sunlight, water, and carbon dioxide to create food and release oxygen.

 

Question 3. .......... gas is given to the patients having breathing problems.
Answer: Oxygen \( (\text{O}_2) \).
In simple words: When people have trouble breathing, doctors give them extra oxygen gas. This helps their bodies get enough air to function.

🎯 Exam Tip: Oxygen masks and concentrators deliver a higher concentration of oxygen than normal air, aiding patients with respiratory distress.

 

Question 4. .......... can be seen moving in a beam of sunlight in a dark room.
Answer: Tiny dust particles.
In simple words: When a sunbeam shines into a dark room, you can see small specks floating around. These are tiny dust particles that become visible when light hits them.

🎯 Exam Tip: This phenomenon, known as the Tyndall effect, happens when light scatters off small particles, making them visible against a dark background.

 

Question 5. .......... gas turns lime water milky.
Answer: Carbon dioxide \( (\text{CO}_2) \).
In simple words: If you blow carbon dioxide gas into limewater, it will turn cloudy or milky. This is a common test to show carbon dioxide is present.

🎯 Exam Tip: The milky appearance is due to the formation of insoluble calcium carbonate when carbon dioxide reacts with calcium hydroxide (limewater).

III. True or False. If False, Give the Correct Statement

 

Question 1. Inhaled air contains a large amount of carbon-di-oxide
Answer: False – Inhaled air contains a large amount of oxygen, not carbon dioxide. We breathe in oxygen and breathe out carbon dioxide.
In simple words: This statement is false because we breathe in air that has mostly oxygen, not a lot of carbon dioxide.

🎯 Exam Tip: Remember that exhaled air has a higher concentration of carbon dioxide than inhaled air, as our bodies produce it during respiration.

 

Question 2. Planting trees help in decreasing global warming
Answer: True. Trees absorb carbon dioxide, a greenhouse gas, helping to reduce its concentration in the atmosphere and thus combat global warming. This process is vital for maintaining Earth's climate.
In simple words: This is true. Trees take in carbon dioxide, which is a gas that causes the Earth to get warmer. So, more trees mean less warming.

🎯 Exam Tip: Always connect tree planting with carbon dioxide absorption and its positive impact on reducing global warming and climate change.

 

Question 3. The composition of air is always exactly the same.
Answer: False – The composition of air changes slightly from place to place and also from season to season. For example, humidity varies a lot.
In simple words: This is false. The amount of different gases in the air can change a little bit depending on where you are or what time of year it is.

🎯 Exam Tip: While the major components (nitrogen, oxygen) are fairly constant, minor components like water vapor and pollutants can cause slight variations in air composition.

 

Question 4. Whales come up to the water surface to breathe in oxygen.
Answer: True. Whales are mammals, and like humans, they have lungs and need to breathe air from the atmosphere, not absorb oxygen from water like fish.
In simple words: This is true. Whales are animals that live in water but need to come to the surface to get air and breathe oxygen.

🎯 Exam Tip: Distinguish between aquatic mammals (like whales and dolphins) that breathe air, and fish that breathe oxygen dissolved in water using gills.

 

Question 5. The balance of oxygen in the atmosphere is maintained through photosynthesis in animals and respiration in plants.
Answer: False – The balance of oxygen in the atmosphere is maintained through photosynthesis in plants and respiration in animals. Photosynthesis releases oxygen, while respiration consumes it.
In simple words: This statement is false. Oxygen balance comes from plants making oxygen (photosynthesis) and animals (and plants) using oxygen (respiration).

🎯 Exam Tip: Understand the complementary roles of photosynthesis (plants producing oxygen) and respiration (all living things using oxygen) in maintaining atmospheric oxygen levels.

IV. Match the Following

 

Question 1. Match the following:

Answer:
1. - c
2. - b
3. - d
4. - e
5. - a
In simple words: This match links words about air and its layers with their correct definitions or related concepts. For instance, moving air is called wind, and the layer we live in is the troposphere.

🎯 Exam Tip: When matching, look for direct definitions or primary associations between the terms to ensure accuracy. Check each pair carefully.

V. Arrange the Following Statements in Correct Sequence

 

Question 1. Arrange the following statements in correct sequence:
1. Plants manufacture food by a process called photosynthesis.
2. Plants require energy for their growth.
3. Plants take in oxygen and release carbon-di-oxide just as animals.
4. Plants take carbon-di-oxide from the atmosphere, use chlorophyll in the presence of sunlight and prepare food.
5. Such oxygen is available to animals and human beings for breathing.
6. During this process, oxygen is released by plants.
Answer:
The correct sequence is:
2. Plants require energy for their growth.
1. Plants manufacture food by a process called photosynthesis.
4. Plants take carbon-di-oxide from the atmosphere, use chlorophyll in the presence of sunlight and prepare food.
6. During this process, oxygen is released by plants.
3. Plants take in oxygen and release carbon-di-oxide just as animals.
5. Such oxygen is available to animals and human beings for breathing.
In simple words: The statements describe the process of photosynthesis and how plants and animals use gases. Plants first need energy, then they make food using sunlight and carbon dioxide, releasing oxygen. Animals then use this oxygen for breathing.

🎯 Exam Tip: For sequencing questions, identify the starting point and the logical flow of events. Photosynthesis is a key process that drives many related biological activities.

VI. Analogy

 

Question 1. Photosynthesis: ........... :: Respiration : Oxygen
Answer: \( \text{CO}_2 \).
In simple words: Just as respiration needs oxygen, photosynthesis needs carbon dioxide to happen. Both are vital gases for these processes.

🎯 Exam Tip: Analogies test your understanding of relationships. Here, the relationship is "input gas required for the process".

 

Question 2. 78% of air : Does not support combustion :: : Supports combustion
Answer: 21% of air.
In simple words: This analogy compares how much of each gas is in the air and what it does in burning. Nitrogen (78%) does not help things burn, while oxygen (21%) does help things burn.

🎯 Exam Tip: Nitrogen is a non-combustible gas, meaning it does not burn or support burning, while oxygen actively promotes combustion.

VII. Observe the Given Figure Carefully and Answer the Questions.

 

Question 1. What will happen if we remove plants from the aquarium?
Answer:
1. The production of \( \text{O}_2 \) and absorption of \( \text{CO}_2 \) and \( \text{NH}_3 \) will be reduced. This means less fresh air and more waste in the water.
2. Plants provide shelter to fish, so, without them, fish may feel insecure or stressed. They also lose hiding spots.
3. Algae growth will increase due to less competition for nutrients from the plants. Algae can then take over the tank.
In simple words: If you take plants out of an aquarium, there will be less fresh air (\( \text{O}_2 \)) for fish, more waste in the water, and fish will have nowhere to hide. Also, more unwanted algae will grow.

🎯 Exam Tip: Aquariums are miniature ecosystems. Understanding how removing one component (plants) affects others (fish, water quality, algae) is key to answering such questions.

 

Question 2. What will happen if we remove the fish from the aquarium and keep it (with green plants) in a dark place?
Answer:
1. Most fishes require both periods of light and darkness. Without fish, the balance of gases will still be affected, and in darkness, plants cannot photosynthesize.
2. In a dark place, plants will lose their green color (pigmentation) over time, and stop growing. They will also start to consume oxygen through respiration without producing any. This means the water's oxygen level would drop.
In simple words: If you take out the fish and keep the aquarium in the dark, the plants will stop making oxygen and start using it up. They will also lose their green color because they need light to grow.

🎯 Exam Tip: Remember that plants perform photosynthesis only in light. In darkness, they also respire, consuming oxygen. Fish are part of the carbon cycle, providing CO2 for plants.

VIII. Give a Very Short Answer

 

Question 1. What is the atmosphere? Name the five layers of the atmosphere.
Answer: Our Earth is surrounded by a huge blanket of air called the atmosphere. This blanket protects us and helps life exist. The atmosphere is made of five different layers – the Troposphere, the Stratosphere, the Mesosphere, the Ionosphere, and the Exosphere.
In simple words: The atmosphere is the big cover of air around Earth. It has five main layers: Troposphere, Stratosphere, Mesosphere, Ionosphere, and Exosphere.

🎯 Exam Tip: Know the order of the atmospheric layers, starting from the closest to Earth: Troposphere, Stratosphere, Mesosphere, Thermosphere (Ionosphere is within this), and Exosphere.

 

Question 2. How do the roots of land plants get oxygen for breathing?
Answer: Oxygen is present in the tiny air spaces found in the soil. Plant roots have very small hairs, called root hairs, which take in this \( \text{O}_2 \) from the soil's air spaces. This happens through a process called diffusion, where gases move from an area of higher concentration to lower concentration.
In simple words: Plant roots get oxygen from the air pockets in the soil. Their root hairs soak up this oxygen to help the plant breathe.

🎯 Exam Tip: Remember that diffusion is the key process for gas exchange in plants, both through stomata in leaves and root hairs in the soil.

 

Question 3. What should be done if the clothes of a person catch fire accidentally? Why?
Answer:
1. First, quickly cover the person in a rug or blanket and tell them to roll on the floor. This action is crucial to suppress the flames.
2. This method works because covering the person cuts off the supply of air (oxygen) to the fire, which is necessary for it to burn. Putting out flames is about removing one side of the fire triangle (fuel, oxygen, heat).
3. A suitable fire extinguisher can also be used if available and safe to do so. This provides an additional layer of safety.
In simple words: If someone's clothes catch fire, cover them with a blanket and make them roll on the floor. This stops the air from reaching the fire and puts it out. A fire extinguisher can also help.

🎯 Exam Tip: The main principle for putting out a fire is to remove one component of the fire triangle (fuel, oxygen, heat). Smothering a fire removes the oxygen supply.

 

Question 4. What will happen if you breathe through your mouth?
Answer: Several health conditions and risk factors can arise from breathing through your mouth instead of your nose.
1. Snoring: Mouth breathing can often lead to snoring.
2. Dry mouth: It causes your mouth to become dry more easily.
3. Daytime tiredness: You might feel tired during the day even after sleeping.
4. Poor dental health: It can affect your teeth and gums, sometimes leading to more cavities.
In simple words: Breathing through your mouth can cause problems like snoring, a dry mouth, feeling tired, and even issues with your teeth. It is always better to breathe through your nose.

🎯 Exam Tip: The nose filters, warms, and humidifies air before it reaches the lungs, which is why nasal breathing is generally healthier than mouth breathing.

IX. Give a Short Answer

 

Question 1. Biscuits kept open on a plate during monsoon days lose their crispness. Why?
Answer: During monsoon days, the air is full of water vapor (humidity). When biscuits are left open, they absorb this water vapor from the atmosphere. This absorption of moisture makes the biscuits soft and causes them to lose their crispness. This is why foods like biscuits are best stored in airtight containers.
In simple words: Biscuits get soft in the monsoon because they soak up water from the humid air. This makes them lose their crunchiness.

🎯 Exam Tip: Foods that absorb moisture from the air are called hygroscopic. Storing such items in airtight containers prevents them from becoming stale or soft.

 

Question 2. Why do traffic assistants wear a mask on duty?
Answer: Traffic assistants work in places where there are many vehicles. They are constantly exposed to the smoke emitted from these vehicles. This smoke contains many harmful pollutants. Inhaling these pollutants can cause breathing problems and other lung diseases. So, they wear a mask to protect their respiratory system from the harmful effects of air pollution.
In simple words: Traffic assistants wear masks to protect themselves from the bad smoke and pollution from cars and bikes. This helps them avoid lung and breathing problems.

🎯 Exam Tip: Masks act as a physical barrier, filtering out harmful particulate matter and pollutants from the air, thus protecting the respiratory system.

X. Answer in Detail

 

Question 1. How do plants and animals maintain the balance of oxygen and carbon-di-oxide in air?
Answer: Plants and animals work together to keep the levels of oxygen and carbon dioxide in the air balanced. This is a natural cycle.
1. Plants, especially those in forests, release oxygen into the air through a process called photosynthesis. This oxygen is then used by animals and humans for breathing (respiration).
2. Animals, during respiration, consume oxygen and release carbon dioxide. Plants then take in this carbon dioxide from the atmosphere. They use it along with sunlight and water to make their own food and release more oxygen. This continuous exchange helps maintain a healthy balance of these essential gases in the atmosphere.
In simple words: Plants make oxygen and take in carbon dioxide. Animals use oxygen and give out carbon dioxide. This constant give-and-take between plants and animals keeps the air clean and balanced for everyone to live.

🎯 Exam Tip: Clearly explain the two main processes – photosynthesis (plants taking CO2, releasing O2) and respiration (animals and plants taking O2, releasing CO2) – and how they form a cycle.

 

Question 2. Why is the atmosphere essential for life on earth?
Answer: The atmosphere is very important for life on Earth because it creates and maintains a suitable climate. It does this by carrying out several key functions:
1. The atmosphere helps keep the Earth's average temperature fairly stable during the day. It prevents the planet from getting too hot or too cold.
2. It stops sudden and extreme increases in temperature during the daytime, acting like a protective shield against the sun's direct heat.
3. It also helps to slow down the escape of heat from the Earth's surface into outer space during the night. This ensures that the Earth stays warm enough for life to survive when the sun is not shining.
In simple words: The atmosphere is vital because it controls Earth's temperature, stopping it from getting too hot or too cold. It acts like a blanket, keeping our planet just right for living things.

🎯 Exam Tip: Focus on the atmosphere's role in temperature regulation and protecting life. Key terms like "greenhouse effect" (though not mentioned, implied) relate to this function.

XI. Questions Based on Higher Order Thinking Skills.

 

Question 1. Can you guess why fire extinguishers throw a stream of carbon-di-oxide while putting - off fire?
Answer: Fire extinguishers use carbon dioxide \( (\text{CO}_2) \) to put out fires because carbon dioxide does not support combustion (burning). When \( \text{CO}_2 \) is sprayed onto a burning object, it creates a thick layer around the fire. This layer cuts off the supply of oxygen from the air, which the fire needs to keep burning. By removing oxygen, the fire is quickly controlled and eventually extinguished. This action efficiently breaks the fire triangle.
In simple words: Fire extinguishers use carbon dioxide because it does not burn and it pushes away the oxygen around a fire. Without oxygen, the fire cannot keep burning and goes out.

🎯 Exam Tip: Carbon dioxide is denser than air, so it effectively blankets the fire, suffocating it by preventing oxygen from reaching the fuel source.

Samacheer Kalvi 6th Science Air Additional Important Questions and Answers

I. Choose the Appropriate Answer

 

Question 1. A layer consisted of water vapour which is responsible for making clouds is.
(a) Stratosphere
(b) Mesosphere
(c) Troposphere
(d) Exosphere
Answer: (c) Troposphere
In simple words: The troposphere is the lowest layer of Earth's atmosphere, where most of the weather, including clouds and rain, happens.

🎯 Exam Tip: The troposphere contains almost all of the atmosphere's water vapor, making it the primary location for cloud formation and weather phenomena.

 

Question 2. ........ is responsible for making clouds.
(a) Hydrogen
(b) Oxygen
(c) Water vapour
(d) Carbon-di-oxide
Answer: (c) Water vapour
In simple words: Water vapor, which is water in a gas form, gathers in the air to make clouds. It is the key ingredient for clouds to form.

🎯 Exam Tip: Clouds form when water vapor in the atmosphere cools and condenses around tiny particles, creating visible droplets or ice crystals.

 

Question 3. A process without emitting flame is called as ........
(a) Combustion
(b) Burning
(c) Cherring
(d) Melting
Answer: (a) Combustion
In simple words: Combustion is the chemical process of burning, which can happen with or without a visible flame. For example, wood can burn slowly without a flame.

🎯 Exam Tip: While all burning is a form of combustion, not all combustion produces a visible flame. Oxidation, like rusting, is a slow form of combustion without flame.

 

Question 4. ........ was able to identify highly reactive gas called oxygen.
(a) Lavoisier
(b) Ingenhousz
(c) Rutherford
(d) Joseph Priestley
Answer: (d) Joseph Priestley
In simple words: Joseph Priestley was the scientist who first found and studied oxygen gas. His discovery was a big step in understanding how things burn and how we breathe.

🎯 Exam Tip: Remember Joseph Priestley for his discovery of oxygen, though Antoine Lavoisier later named it and correctly described its role in combustion.

 

Question 5. Which is used in refrigerating meat and fish?
(a) Liquid Ammonia
(b) Liquid Nitrogen
(c) Solid \( \text{CO}_2 \)
(d) Helium
Answer: (c) Solid \( \text{CO}_2 \)
In simple words: Solid carbon dioxide, also called dry ice, is very cold and is used to keep things like meat and fish frozen for a long time. It sublimates (turns directly into gas) without leaving any liquid mess.

🎯 Exam Tip: Dry ice (\( \text{CO}_2 \) solid) is preferred for freezing certain items because it maintains a very low temperature and does not melt into a liquid, preventing water damage.

II. True or False. If False, Give the Correct Statement

 

Question 1. Oxygen is used for the synthesis of protein and fertilizers.
Answer: False – Nitrogen is primarily used for the synthesis of proteins and fertilizers, not oxygen. Nitrogen is a key component of amino acids and nucleic acids.
In simple words: This is false. Nitrogen, not oxygen, is the main gas used to make proteins and plant fertilizers.

🎯 Exam Tip: Nitrogen fixation (converting atmospheric nitrogen into usable forms) is essential for plant growth and the production of proteins.

 

Question 2. \( \text{CO}_2 \) turns calcium hydroxide solution to a milky white solution.
Answer: True. This is a common chemical test to detect the presence of carbon dioxide. The milky appearance is due to calcium carbonate formation.
In simple words: This is true. When carbon dioxide gas is put into limewater (calcium hydroxide solution), it turns white and cloudy.

🎯 Exam Tip: The reaction is \( \text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 \downarrow + \text{H}_2\text{O} \), where \( \text{CaCO}_3 \) (calcium carbonate) is the insoluble white precipitate.

 

Question 3. The air in coastal areas have more oxygen.
Answer: False – The air in coastal areas has more water vapor (humidity), not necessarily more oxygen. Oxygen levels are generally consistent globally.
In simple words: This is false. Air near the sea has more moisture, but not more oxygen than other places.

🎯 Exam Tip: Humidity is a measure of water vapor in the air, which is typically higher near large bodies of water like oceans due to evaporation.

 

Question 4. The role of chlorophyll is to absorb light from the sun.
Answer: True. Chlorophyll is the green pigment in plants that captures sunlight energy, which is essential for photosynthesis. It is crucial for the plant's food-making process.
In simple words: This is true. Chlorophyll is the green stuff in plants that soaks up sunlight, helping the plant make its own food.

🎯 Exam Tip: Chlorophyll is vital for photosynthesis, converting light energy into chemical energy, and is responsible for the green color of plants.

 

Question 5. When cooled to -57°C, gaseous carbon-di-oxide becomes a liquid.
Answer: False – When cooled to -57°C, gaseous carbon dioxide becomes a solid (dry ice) through a process called deposition, not a liquid. This is why it is called "dry" ice.
In simple words: This is false. When carbon dioxide gets very cold at -57°C, it turns directly into a solid, not a liquid. We call this dry ice.

🎯 Exam Tip: Carbon dioxide bypasses the liquid state at standard atmospheric pressure, going directly from gas to solid (deposition) or solid to gas (sublimation).

III. Match the Following

 

Question 1. Match the following:

Answer:
i. - c
ii. - d
iii. - a
iv. - b
In simple words: This match connects events or features with the specific layers of the atmosphere where they occur. For example, meteors burn in the mesosphere, and weather changes happen in the troposphere.

🎯 Exam Tip: Knowing the characteristics and phenomena associated with each atmospheric layer is essential for matching questions like this. Review the key features of each layer.

IV. Give Very Short Answer

 

Question 1. Where does Ozone layer lie?
Answer: The ozone layer is located in the stratosphere, which is one of the upper layers of the atmosphere, lying above the troposphere. This layer protects Earth from harmful UV radiation. It is like Earth's natural sunscreen.
In simple words: The ozone layer is found in the stratosphere, which is a layer of air high above the Earth.

🎯 Exam Tip: Emphasize that the ozone layer's main function is to absorb harmful ultraviolet (UV) radiation from the sun, protecting life on Earth.

 

Question 2. "Air is not an elementary substance, but a composition". Why?
Answer: Air is not an elementary substance (meaning a single pure element) because it is a composite mixture. This means it is made up of many different gases that are combined physically, not chemically. It contains various gases like nitrogen \( (\text{N}_2) \), oxygen \( (\text{O}_2) \), carbon dioxide \( (\text{CO}_2) \), and others, all mixed together but not bonded to each other. We can separate these gases easily.
In simple words: Air is not just one thing; it is a mix of many gases like nitrogen, oxygen, and carbon dioxide. These gases are mixed but not joined together like in a compound, which is why it is a composition.

🎯 Exam Tip: Distinguish between elements (like pure oxygen), compounds (like water), and mixtures (like air) to understand why air is a composition.

 

Question 3. Mention the percentage composition of Air.
Answer: The air around us is primarily composed of:

These percentages are important for supporting life and various natural processes on Earth.
In simple words: Air is mostly nitrogen (78%) and oxygen (21%). A very small part (1%) is made up of other gases like carbon dioxide, argon, and water vapor.

🎯 Exam Tip: Memorize the approximate percentages of nitrogen, oxygen, and other gases in the atmosphere, as this is a fundamental concept in environmental science.

 

Question 4. What is Burning?
Answer: Burning, also known as combustion, is a rapid chemical process where a substance reacts with oxygen. This reaction releases a large amount of energy, usually in the form of light and heat. It is a fundamental process, powering many things from candles to engines.
In simple words: Burning is when something quickly reacts with oxygen, giving off a lot of light and heat.

🎯 Exam Tip: Remember the three components of the "fire triangle": fuel, oxygen, and heat. Burning occurs when all three are present.

 

Question 5. Define – Combustion. Give an example.
Answer: Combustion is a chemical process where a substance reacts with oxygen, usually producing heat and light. It is often called burning. Sometimes, combustion can happen without a visible flame. For example, rocket propellants (fuel mixed with oxygen) undergo rapid combustion to produce thrust, without necessarily showing a visible flame outside the engine.
In simple words: Combustion is the process of burning, which involves a substance reacting with oxygen to create heat and light. An example is rocket fuel burning quickly inside an engine.

🎯 Exam Tip: Differentiate between "burning" (which usually implies a flame) and "combustion" (the chemical process, which might not always produce a visible flame).

V. Answer in Detail

 

Question 1. Briefly explain the process of 'Photo Synthesis'.
Answer: Photosynthesis is the amazing process by which plants make their own food, essentially powering life on Earth. Here is how it works:
1. Plants use special green pigment called chlorophyll, mostly found in their leaves, to capture energy from sunlight.
2. They take in carbon dioxide \( (\text{CO}_2) \) from the air and water \( (\text{H}_2\text{O}) \) from the soil through their roots.
3. Using the absorbed sunlight energy, chlorophyll helps these raw materials ( \( \text{CO}_2 \) and \( \text{H}_2\text{O} \)) react to produce food (sugars for energy) and oxygen \( (\text{O}_2) \) as a byproduct. The simplified reaction is: \( \text{CO}_2 + \text{H}_2\text{O} \xrightarrow{\text{Sunlight, Chlorophyll}} \text{Food} + \text{O}_2 \uparrow \).
4. The oxygen released during photosynthesis is much more than what the plants themselves consume for their own respiration. This extra oxygen is then released into the atmosphere, making it available for animals and humans to breathe.
In simple words: Photosynthesis is how plants make food. They use sunlight, water, and carbon dioxide to create sugars for themselves and release oxygen into the air. Chlorophyll is the green stuff that helps catch sunlight.

🎯 Exam Tip: Make sure to mention all key ingredients (carbon dioxide, water, sunlight) and products (food/glucose, oxygen) for photosynthesis, and the role of chlorophyll.

 

Question 2. Mention the uses of Air.
Answer: Air is essential for many reasons and has numerous uses vital for life and human activities:
1. Breathing: Both plants and animals need air (specifically oxygen) to breathe and survive. This is fundamental for respiration, which generates energy for living organisms.
2. Combustion: Air (oxygen) is required for burning fuels like wood, coal, kerosene, and LPG. These fuels provide heat and energy for various purposes, from cooking to powering vehicles.
3. Compressed Air: Compressed air is widely used, for instance, to fill vehicle tires, power pneumatic tools, and operate machinery.
4. Water Cycle: Air plays a critical role in maintaining the water cycle in nature. It helps in the evaporation of water and carries water vapor, leading to cloud formation and precipitation. This unique property of air ensures that water is recycled across the planet.
5. Medical and Industrial Uses: Oxygen gas is used in hospitals for patients with breathing difficulties, by climbers in mountains, and by divers in the deep sea. It is also essential for many industrial processes.
In simple words: Air is super important for many things. We need it to breathe, and it helps things burn. Compressed air fills tires, and air helps water move around the Earth (water cycle). Also, oxygen from the air is used by sick people and adventurers.

🎯 Exam Tip: When listing uses of air, categorize them into broad areas like biological, industrial, and environmental to ensure comprehensive coverage. Remember the composition of air and its properties.

Samacheer Kalvi 6th Science Air Text Book Back Questions and Answers

I. Choose the correct answer:

 

Question 1. .......... is the percentage of nitrogen in the air.
(a) 78%
(b) 21%
(c) 0.03%
(d) 1%
Answer: (a) 78%
In simple words: Nitrogen makes up the biggest part of the air we breathe, about 78%. This gas is very important for life on Earth.

🎯 Exam Tip: Remember the main gases in air and their percentages, especially nitrogen and oxygen, as these are fundamental facts about our atmosphere.

 

Question 2. Gas exchange takes place in plants using ..........
(a) Stomata
(b) Chlorophyll
(c) Leaves
(d) Flowers
Answer: (a) Stomata
In simple words: Plants breathe through tiny holes, mostly on their leaves, called stomata. These small openings let gases like carbon dioxide and oxygen move in and out.

🎯 Exam Tip: Focus on key plant structures and their functions, such as stomata for gas exchange and chlorophyll for making food.

 

Question 3. The constituent of air that supports combustion is ..........
(a) Nitrogen
(b) carbon-di-oxide
(c) Oxygen
(d) water vapour
Answer: (c) Oxygen
In simple words: Oxygen is the gas in the air that helps things burn. Without oxygen, fires cannot start or keep burning.

🎯 Exam Tip: Understand the role of different gases in common processes like combustion and photosynthesis. Oxygen is crucial for burning.

 

Question 4. Nitrogen is used in the food packaging industry because it ..........
(a) provides colour to the food
(b) provides oxygen to the food
(c) adds proteins and minerals to the food
(d) keeps the food fresh
Answer: (d) keeps the food fresh
In simple words: Nitrogen gas is put into food packets to stop food from going bad quickly. It prevents oxygen from reaching the food, which slows down spoilage.

🎯 Exam Tip: Consider the practical applications of common gases, such as nitrogen's use as a preservative in food packaging due to its inert nature.

 

Question 5. .......... and .......... are the two gases, which when taken together, make up about 99 percentage of air.
I. Nitrogen
II. carbon-di-oxide
III. Noble gases
IV. Oxygen
(a) I and II
(b) I and III
(c) II and IV
(d) I and IV
Answer: (d) I and IV
In simple words: Nitrogen and oxygen together make up most of the air, almost 99 percent. These two gases are the most important parts of the atmosphere.

🎯 Exam Tip: Know the primary components of air and their approximate percentages. Nitrogen and oxygen are the dominant gases.

II. Fill in the blanks

 

Question 1. .......... is the active component of air.
Answer: Oxygen (O₂)
In simple words: Oxygen is called the active part of air because it takes part in many important reactions like burning and breathing. This is why it is essential for life.

🎯 Exam Tip: Understand that "active component" means the part that readily reacts or is used in processes like respiration and combustion.

 

Question 2. The gas given out during photosynthesis is ..........
Answer: Oxygen (O₂)
In simple words: During photosynthesis, plants use sunlight, water, and carbon dioxide to make their own food, and they release oxygen as a byproduct. This oxygen is vital for animals and humans.

🎯 Exam Tip: Remember that photosynthesis is the process where plants produce food and release oxygen, which is essential for most living things to breathe.

 

Question 3. .......... gas is given to the patients having breathing problems.
Answer: Oxygen (O₂)
In simple words: People who have trouble breathing are often given extra oxygen. This helps their bodies get enough oxygen to function properly.

🎯 Exam Tip: Oxygen therapy is a common medical treatment for respiratory issues, highlighting the life-sustaining role of this gas.

 

Question 4. .......... can be seen moving in a beam of sunlight in a dark room.
Answer: Tiny dust particles
In simple words: When a beam of sunlight shines into a dark room, you can see small specks floating around. These are tiny dust particles that become visible when light reflects off them.

🎯 Exam Tip: This phenomenon, known as the Tyndall effect, shows that air is not perfectly clear but contains small suspended particles.

 

Question 5. .......... gas turns lime water milky.
Answer: Carbon dioxide (CO₂)
In simple words: If you bubble carbon dioxide gas through clear lime water, the water will turn cloudy or milky. This is a common test to show if carbon dioxide is present.

🎯 Exam Tip: The lime water test is a classic indicator for the presence of carbon dioxide due to the formation of calcium carbonate.

III. True or False. If False, give the correct statement

 

Question 1. Inhaled air contains a large amount of carbon-di-oxide
Answer: False – (Inhaled air contains a large amount of oxygen)
In simple words: When we breathe in, we take in air that has mostly oxygen, not a lot of carbon dioxide. Our bodies need oxygen to work.

🎯 Exam Tip: Distinguish between inhaled air, which is rich in oxygen, and exhaled air, which has a higher concentration of carbon dioxide.

 

Question 2. Planting trees help in decreasing global warming
Answer: True
In simple words: Planting more trees helps to reduce global warming. Trees absorb carbon dioxide, which is a greenhouse gas, from the atmosphere.

🎯 Exam Tip: Emphasize the role of trees in absorbing carbon dioxide, thereby mitigating the greenhouse effect and climate change.

 

Question 3. The composition of air is always exactly the same.
Answer: False – (The composition of air changes slightly from place to place & also from season to season)
In simple words: The air's makeup is mostly the same everywhere, but it can change a little bit depending on the place or time of year. For example, some places might have more water vapor.

🎯 Exam Tip: While the major components of air are constant, minor variations in factors like humidity, pollutants, and altitude can alter its exact composition locally.

 

Question 4. Whales come up to the water surface to breathe in oxygen.
Answer: True
In simple words: Whales are mammals, just like humans, and they need to breathe air to get oxygen. They regularly come to the water's surface for this purpose.

🎯 Exam Tip: Highlight that marine mammals, despite living in water, are air-breathers and must surface to exchange gases.

 

Question 5. The balance of oxygen in the atmosphere is maintained through photosynthesis in animals and respiration in plants.
Answer: False – (The balance of oxygen in the atmosphere is maintained through Photosynthesis in plants & respiration in animals)
In simple words: The right amount of oxygen in the air stays balanced because plants make oxygen through photosynthesis, and animals use oxygen during respiration. Plants produce what animals need, and animals produce what plants need.

🎯 Exam Tip: Clearly explain the interconnected cycle of oxygen and carbon dioxide involving photosynthesis by plants and respiration by animals to maintain atmospheric balance.

IV. Match the following

 

Answer:
1. - c
2. - b
3. - d
4. - e
5. - a
In simple words: This matching exercise connects common terms about air and its layers with their correct definitions or related concepts. For example, moving air is called wind, and oxygen helps things burn.

🎯 Exam Tip: Carefully read each item in both columns and try to recall definitions or associations. Pay attention to specific terms related to atmospheric layers and gas functions.

V. Arrange the following statements in correct sequence

 

Question 1. Arrange the following statements in correct sequence
1. Plants manufacture food by a process called photosynthesis.
2. Plants require energy for their growth.
3. Plants take in oxygen and release carbon-di-oxide just as animals.
4. Plants take carbon-di-oxide from the atmosphere, use chlorophyll in the presence of sunlight and prepare food.
5. Such oxygen is available to animals and human beings for breathing.
6. During this process, oxygen is released by plants.
Answer:
2. Plants require energy for their growth.
1. Plants manufacture food by a process called photosynthesis.
6. During this process, oxygen is released by plants.
3. Plants take in oxygen and release carbon-di-oxide just as animals.
5. Such oxygen is available to animals and human beings for breathing.
4. Plants take carbon-di-oxide from the atmosphere, use chlorophyll in the presence of sunlight and prepare food.
In simple words: The correct order explains how plants grow, make food using sunlight, release oxygen, and how oxygen is then used by animals and for plant respiration. This shows the flow of energy and gases in nature.

🎯 Exam Tip: To sequence events, identify the starting point and then logically follow the cause-and-effect relationships or chronological order of the steps involved in a process.

VI. Analogy

 

Question 1. Photosynthesis: .......... :: Respiration : Oxygen
Answer: CO₂
In simple words: Just as oxygen is needed for respiration, carbon dioxide is needed for photosynthesis. Both processes are essential for life.

🎯 Exam Tip: In analogy questions, find the relationship between the first pair of words and apply the same relationship to the second pair.

 

Question 2. 78% of air : Does not support combustion :: .......... : Supports combustion
Answer: 21% of air
In simple words: This analogy shows that while the large amount of nitrogen (78%) in the air does not help things burn, the smaller amount of oxygen (21%) is what makes burning possible.

🎯 Exam Tip: Identify the key property of each component mentioned in the analogy (e.g., nitrogen's inertness vs. oxygen's role in combustion).

VII. Observe the given figure carefully and answer the questions.

 

Question 1. What will happen if we remove plants from the aquarium?
Answer:
1. The production of O₂ and absorption of CO₂ and NH₃ will be reduced.
2. Plants provide shelter to fish, so, they will feel insecure.
3. Algae growth will increase.
In simple words: If you take plants out of an aquarium, there will be less oxygen for fish, more carbon dioxide and ammonia, and the fish might feel unsafe. Also, unwanted algae could grow more easily.

🎯 Exam Tip: Think about the role of plants in an aquatic ecosystem: they produce oxygen, absorb waste products, and provide shelter, all crucial for balance.

 

Question 2. What will happen if we remove the fish from the aquarium and keep it (with green plants) in a dark place?
Answer:
1. Most of the fishes require both periods of light and darkness.
2. In a dark place, they will lose their sight and pigmentation.
In simple words: If you take fish out of an aquarium and put them (with plants) in the dark, they will not get enough light which is important for them. This will make them lose their color and hurt their eyesight.

🎯 Exam Tip: Consider the importance of light for aquatic life, not just for photosynthesis but also for the general health, vision, and natural coloration of fish.

VIII. Give a very short Answer

 

Question 1. What is the atmosphere? Name the five layers of the atmosphere.
Answer: Our earth is surrounded by a huge envelope of air called the atmosphere. The atmosphere is made of five different layers – the Troposphere, the Stratosphere, the Mesosphere, the Ionosphere, and the Exosphere. This blanket of air is vital for supporting life on Earth.
In simple words: The atmosphere is the big layer of air around our Earth. It has five main parts: Troposphere, Stratosphere, Mesosphere, Ionosphere, and Exosphere.

🎯 Exam Tip: Be able to define the atmosphere and list its main layers in order. Each layer has unique characteristics and importance.

 

Question 2. How do the roots of land plants get oxygen for breathing?
Answer: Oxygen is present in the air spaces of soil. This O₂ is taken by root hairs through diffusion to the rest of the plant. Plant roots also need to breathe to survive, just like humans.
In simple words: Plant roots get oxygen from the small gaps of air in the soil. Tiny root hairs soak up this oxygen and send it to the rest of the plant.

🎯 Exam Tip: Remember that even underground, plant roots perform respiration and require oxygen, which they absorb from the air pockets in the soil.

 

Question 3. What should be done if the clothes of a person catch fire accidentally? Why?
Answer:
1. Cover the person in a rug or blanket and roll them on the floor.
2. This will cut off the air and put out the flames.
3. A suitable fire extinguisher can also be chosen. The main goal is to remove oxygen, which fuels the fire.
In simple words: If someone's clothes catch fire, quickly cover them with a blanket and roll them on the ground. This stops the oxygen from reaching the fire, which makes the fire go out.

🎯 Exam Tip: Focus on the principle of removing oxygen to extinguish a fire (the "Smothering" method). "Stop, Drop, and Roll" is also a key safety procedure.

 

Question 4. What will happen if you breathe through your mouth?
Answer: Several health conditions and risk factors can lead to mouth breathing.
1. Snoring
2. dry mouth
3. daytime tiredness
4. Poor dental health. The nose acts as a filter and humidifier for inhaled air.
In simple words: Breathing through your mouth can cause problems like snoring, dry mouth, feeling tired during the day, and bad dental health. Our nose is designed to filter and warm the air we breathe.

🎯 Exam Tip: Understand that nasal breathing is healthier as the nose filters, warms, and humidifies air, protecting the respiratory system.

IX. Give a short answer

 

Question 1. Biscuits kept open on a plate during monsoon days lose their crispness. Why?
Answer: During monsoon days, water vapour from the atmosphere is absorbed in the biscuits. So the biscuits lose their crispness. The air during monsoons is often very humid, causing many dry foods to become soft.
In simple words: On rainy monsoon days, biscuits get soft because they soak up water from the moist air. This makes them lose their crunchy texture.

🎯 Exam Tip: This illustrates the concept of hygroscopy, where substances absorb moisture from the air, especially in humid conditions.

 

Question 2. Why do traffic assistants wear a mask on duty?
Answer: Traffic assistants are continually exposed to smoke emitted from vehicles. Inhaling the pollutants in the smoke may cause breathing and lung problems. So they wear a mask on duty. These masks help filter out tiny harmful particles, making the air they breathe much cleaner.
In simple words: Traffic assistants wear masks to protect their lungs from the harmful smoke and pollutants that come from vehicles on the road. This helps prevent breathing problems.

🎯 Exam Tip: Emphasize the health risks of air pollution from vehicle exhaust and the protective role of masks in reducing exposure to particulate matter.

X. Answer in detail

 

Question 1. How do plants and animals maintain the balance of oxygen and carbon-di-oxide in air?
Answer:
1. Plants in forests release oxygen through the process of photosynthesis and help in providing oxygen to animals for respiration.
2. Plants consume carbon dioxide released by the animals. In this way, plants help in maintaining a balance of oxygen and carbon dioxide in the atmosphere. This continuous exchange forms a vital cycle for life.
In simple words: Plants make oxygen when they do photosynthesis, which animals breathe. Animals breathe out carbon dioxide, which plants use. This give-and-take keeps oxygen and carbon dioxide balanced in the air.

🎯 Exam Tip: Describe the oxygen-carbon dioxide cycle by explaining how photosynthesis (plants taking in CO₂, releasing O₂) and respiration (animals taking in O₂, releasing CO₂) are complementary processes.

 

Question 2. Why is the atmosphere essential for life on earth?
Answer: The atmosphere is essential for life because it maintains an appropriate climate for the maintenance of life by carrying out the following activities:
1. The atmosphere keeps the average temperature of the Earth fairly constant during the day time.
2. It prevents a sudden increase in temperature during the day time.
3. It also slows down the escape of heat from the surface of the Earth into outer space during the night time. This creates stable conditions necessary for ecosystems to thrive.
In simple words: The air around Earth, called the atmosphere, is very important for life. It keeps the planet at a good temperature, stopping it from getting too hot in the day or too cold at night.

🎯 Exam Tip: Focus on the atmosphere's role in temperature regulation (greenhouse effect), providing breathable gases, and protecting from harmful radiation.

XI. Questions Based on Higher Order Thinking Skills.

 

Question 1. Can you guess why fire extinguishers throw a stream of carbon-di-oxide while putting - off fire?
Answer: It is because carbon-di-oxide (CO₂) does not support combustion. When sprayed on burning object it stops the supply of oxygen and controls the fire. Carbon dioxide is heavier than air, so it forms a blanket over the fire, effectively suffocating it.
In simple words: Fire extinguishers use carbon dioxide gas because it does not help things burn. When sprayed on a fire, it covers the burning item, stopping oxygen from reaching it and putting the fire out.

🎯 Exam Tip: Explain that carbon dioxide acts by cutting off the oxygen supply to the fire, which is one of the three components needed for combustion (fuel, oxygen, heat).

Samacheer Kalvi 6th Science Air Additional Important Questions and Answers

I. Choose the appropriate answer

 

Question 1. A layer consisted of water vapour which is responsible for making clouds is.
(a) Stratosphere
(b) Mesosphere
(c) Troposphere
(d) Exosphere
Answer: (c) Troposphere
In simple words: The troposphere is the lowest layer of the atmosphere, where most weather happens and clouds are formed. This is because it holds most of the water vapor.

🎯 Exam Tip: Remember that the troposphere is where all weather phenomena, including cloud formation and rainfall, occur.

 

Question 2. .......... is responsible for making clouds.
(a) Hydrogen
(b) Oxygen
(c) Water vapour
(d) Carbon-di-oxide
Answer: (c) Water vapour
In simple words: Water vapor, which is water in its gas form, is the main thing that makes clouds. When water vapor cools down, it turns into tiny water droplets or ice crystals that form clouds.

🎯 Exam Tip: Understand that water vapor is crucial for the water cycle and cloud formation, which are key elements of Earth's weather system.

 

Question 3. A process without emitting flame is called as ..........
(a) Combustion
(b) Burning
(c) Cherring
(d) Melting
Answer: (a) Combustion
In simple words: Combustion is a rapid chemical reaction that produces heat and light. It can happen without a visible flame, such as when iron rusts slowly.

🎯 Exam Tip: Differentiate between burning (combustion with a flame) and combustion without a flame, recognizing that both are oxidation processes.

 

Question 4. .......... was able to identify highly reactive gas called oxygen.
(a) Lavoisier
(b) Ingenhousz
(c) Rutherford
(d) Joseph Priestley
Answer: (d) Joseph Priestley
In simple words: Joseph Priestley was an important scientist who discovered oxygen, a very active gas. His work helped us understand more about air and how it works.

🎯 Exam Tip: Recall important historical figures and their contributions to science, especially in the discovery of key elements and gases.

 

Question 5. Which is used in refrigerating meat and fish?
(a) Liquid Ammonia
(b) Liquid Nitrogen
(c) Solid CO₂
(d) Helium
Answer: (c) solid CO₂
In simple words: Solid carbon dioxide, also known as dry ice, is used to keep meat and fish very cold. It changes directly into a gas without melting, making it a good coolant.

🎯 Exam Tip: Recognize the properties of dry ice (solid CO₂) like sublimation and its application in refrigeration due to its extremely low temperature.

II. True or False. If False, give the correct statement

 

Question 1. Oxygen is used for the synthesis of protein and fertilizers.
Answer: False – (Nitrogen is used for the synthesis of protein and fertilizers)
In simple words: Nitrogen, not oxygen, is the gas that is used to make proteins and fertilizers. Nitrogen is a key building block for living things and plant food.

🎯 Exam Tip: Understand the specific roles of different elements in biological and industrial processes; nitrogen is fundamental for proteins and fertilizers.

 

Question 2. CO₂ turns calcium hydroxide solution to a milky white solution.
Answer: True
In simple words: When carbon dioxide mixes with calcium hydroxide solution (lime water), it forms a white cloudy substance. This reaction is a common way to test for carbon dioxide.

🎯 Exam Tip: Remember the chemical test for carbon dioxide (passing it through limewater) and the resulting cloudy precipitate of calcium carbonate.

 

Question 3. The air in coastal areas have more oxygen.
Answer: False - (The air in coastal areas have more water vapour)
In simple words: Air near the sea has more water vapor, making it humid, rather than more oxygen. The amount of oxygen in the atmosphere stays quite constant everywhere.

🎯 Exam Tip: Differentiate between the percentage of oxygen, which is relatively stable globally, and humidity, which varies significantly with location and climate.

 

Question 4. The role of chlorophyll is to absorb light from the sun.
Answer: True
In simple words: Chlorophyll is the green pigment in plants that captures sunlight. This captured sunlight energy is then used by the plant to make food through photosynthesis.

🎯 Exam Tip: Chlorophyll is the key molecule for photosynthesis, acting as the primary light-absorbing pigment in plants.

 

Question 5. When cooled to -57°C, gaseous carbon-di-oxide becomes a liquid.
Answer: False – (When cooled to -57°C, gaseous carbon-di-oxide becomes a solid)
In simple words: If you cool carbon dioxide gas down to -57°C, it skips the liquid stage and turns directly into a solid, which is known as dry ice. This process is called sublimation.

🎯 Exam Tip: Note that carbon dioxide sublimes, meaning it goes directly from a gas to a solid (and vice versa) without passing through a liquid phase at atmospheric pressure.

III. Match the following

 

Answer:
i. - c
ii. - d
iii. - a
iv. – b
In simple words: This exercise matches different atmospheric phenomena and features to the correct layers of the atmosphere. For example, meteors burn up in the mesosphere, and the ozone layer is in the stratosphere.

🎯 Exam Tip: Understand the key characteristics and events associated with each layer of the atmosphere to correctly match them.

IV. Give very short answer

 

Question 1. Where does Ozone layer lie?
Answer: The ozone layer is present in the stratosphere, which lies above the troposphere. This layer protects Earth from harmful ultraviolet radiation.
In simple words: The ozone layer is found in the stratosphere, which is a layer of air above the one we live in.

🎯 Exam Tip: Remember that the stratosphere hosts the ozone layer, which is crucial for absorbing harmful UV radiation from the sun.

 

Question 2. "Air is not an elementary substance, but a composition". Why?
Answer: Air is a composite mixture of many gases like N₂, O₂, CO₂ and others. Because it is made of different substances combined together, it is called a composition, not a single element.
In simple words: Air is a mixture because it is made of many different gases mixed together, like nitrogen, oxygen, and carbon dioxide, not just one simple substance.

🎯 Exam Tip: Understand the difference between an element (a single type of atom), a compound (different atoms chemically bonded), and a mixture (different substances physically combined).

 

Question 3. Mention the percentage composition of Air.
Answer:

This table shows the primary gases that make up the Earth's atmosphere and their approximate proportions.
In simple words: Air is mostly nitrogen (about 78%) and oxygen (about 21%). The remaining 1% is made up of other gases like carbon dioxide, argon, and water vapor.

🎯 Exam Tip: Memorize the approximate percentages of the major gases in the atmosphere, especially nitrogen and oxygen.

 

Question 4. What is Burning?
Answer: Burning is the process of rapid firing of a substance in the presence of O₂ and releasing a large amount of light and heat. It is a chemical reaction known as combustion.
In simple words: Burning is when something quickly reacts with oxygen, producing a lot of light and heat. It is a type of chemical reaction.

🎯 Exam Tip: Define burning as a form of combustion, emphasizing the need for oxygen and the production of heat and light.

 

Question 5. Define – Combustion. Give an example.
Answer: Combustion is the process of firing which does not emit flame (fire without flame). Ex: Rocket propellants (fuel with oxygen). Combustion is a chemical process where a substance reacts with an oxidant, usually oxygen, to release energy as heat and light.
In simple words: Combustion is a fast chemical process that makes heat and light. It does not always have a flame. For example, rocket fuels burn very quickly with oxygen but without a visible flame.

🎯 Exam Tip: Distinguish between general combustion (which includes flameless reactions) and burning (combustion with a visible flame).

V. Answer in detail

 

Question 1. Briefly explain the process of 'Photo Synthesis'.
Answer:
1. Plants manufacture their food by 'Photosynthesis'.
2. CO₂ from the air and water from the soil react in the presence of sunlight to produce food.
\[ CO_2 + H_2O \xrightarrow{\text{Sunlight}} \text{Food} + O_2\uparrow \] 3. Chlorophyll absorbs light from the sun.
4. The liberated O₂ during photosynthesis is much more than the O₂ consumed by the plants for respiration. This process is the foundation of most food chains on Earth.
In simple words: Photosynthesis is how plants make their own food. They use carbon dioxide from the air, water from the soil, and sunlight. Chlorophyll in the leaves helps to capture sunlight. During this, plants release oxygen, which we breathe.

🎯 Exam Tip: Understand the inputs (CO₂, water, sunlight), outputs (food, O₂), and key components (chlorophyll) of photosynthesis and its chemical equation.

 

Question 2. Mention the uses of Air.
Answer:
1. For breathing by plants and Animals.
2. For burning fuels like wood, coal, kerosene, LPG etc.,.
3. Compressed air is used to fill tyres of vehicles.
4. Maintaining the water cycle in nature. Because air contains water vapor, which is essential for rain.
5. O₂ gas is used by patients in Hospitals, Climbers in mountains, Divers in Deepsea. Air is a fundamental resource that enables various biological, industrial, and environmental processes.
In simple words: Air is used for many things: living beings breathe it, fuels burn in it, compressed air fills vehicle tires, and it helps with the water cycle. Oxygen from the air is also given to sick people, mountain climbers, and deep-sea divers.

🎯 Exam Tip: List both the biological (respiration), physical (wind, pressure), and chemical (combustion) uses of air and its components, and also its role in the water cycle.