CBSE Class 6 Science Air and Atmosphere Worksheet Set 10

Answer: (b) Nitrogen. Nitrogen makes up about 78% of air by volume.

Teacher's Note:
1. Oxygen is only about 21% of air.
2. Remember the order: nitrogen, oxygen, then small amounts of other gases.

Answer: (a) mixture of gases. Its components are simply mixed and keep their own properties; they can vary in amount from place to place.

Teacher's Note:
1. A mixture has no fixed ratio of its parts, unlike a compound.
2. Air can be separated into its gases by physical methods.

Answer: (b) Oxygen. Oxygen supports combustion; fuels burn only when oxygen is available.

Teacher's Note:
1. Nitrogen and carbon dioxide do not support burning.
2. This is why a candle goes out in a closed jar.

Answer: (c) Carbon dioxide. Plants use carbon dioxide, water and sunlight in photosynthesis.

Teacher's Note:
1. Oxygen is released during photosynthesis.
2. Do not confuse this with respiration, where oxygen is used.

Answer: (b) human activity. Smoke from vehicles, factories and burning of waste adds harmful substances to air.

Teacher's Note:
1. Natural events such as volcanoes also pollute, but the main cause today is human activity.
2. Reducing our use of fuels helps keep air clean.

Answer: (c) CNG. Compressed natural gas burns more cleanly and gives out less smoke than coal, wood or diesel.

Teacher's Note:
1. Many city buses and auto-rickshaws now run on CNG.
2. Cleaner fuels lower the harmful gases and particles released into air.

Answer: (c) Carbon dioxide. Carbon dioxide reacts with lime water to form a white, milky substance.

Teacher's Note:
1. Exhaled air turns lime water milky faster than fresh air does.
2. This is the standard test for carbon dioxide.

Answer: Atmosphere. The atmosphere is held around the Earth by gravity.

Teacher's Note:
1. It protects living things and supplies the gases they need.
2. It becomes thinner as we go higher.

Answer: space; mass (weight). A balloon takes up space when filled with air, and a filled balloon weighs a little more than an empty one.

Teacher's Note:
1. Anything that has mass and takes up space is matter.
2. So air is a form of matter.

Answer: mixture. Nitrogen, oxygen, carbon dioxide and other gases are present together.

Teacher's Note:
1. They are not chemically joined.
2. The proportions can change a little with place and time.

Answer: 21. Nitrogen is about 78%, oxygen about 21%, and carbon dioxide, argon and other gases make up the remaining 1% or so.

Teacher's Note:
1. Water vapour and dust are also present in varying amounts.
2. Learn the two main numbers: 78 and 21.

Answer: oxygen. Without oxygen, fuels cannot burn.

Teacher's Note:
1. Fire needs fuel, heat and oxygen.
2. Cutting off oxygen is how many fires are put out.

Answer: False. Air is a mixture, not a compound.

Teacher's Note:
1. In a compound the elements are chemically combined in a fixed ratio.
2. The gases in air are only mixed.

Answer: False. Air can be compressed because there is a lot of empty space between its particles.

Teacher's Note:
1. Compressed air is used to fill tyres.
2. Solids and liquids are much harder to compress.

Answer: True. About 78% of air is nitrogen.

Teacher's Note:
1. It is far more abundant than oxygen.
2. Nitrogen does not support burning.

Answer: False. Polluted air contains smoke, dust and harmful gases that can cause breathing problems.

Teacher's Note:
1. It can harm the lungs and eyes.
2. Clean air is essential for good health.

Answer: False. Too much dust causes coughing, allergies and breathing trouble.

Teacher's Note:
1. Dust is one of the pollutants in air.
2. People with asthma are affected most.

Answer: 1-b; 2-c; 3-a; 4-e; 5-d.

Teacher's Note:
1. Oxygen supports burning, and nitrogen (through compounds in the soil) helps plants grow.
2. Water vapour is what makes the air humid.

Answer: Air is made of several gases, mainly nitrogen and oxygen, mixed in no fixed ratio. The gases keep their own properties and can be separated by physical methods, so air is a mixture.

Teacher's Note:
1. A mixture can have varying amounts of its parts.
2. Always give both the reason and an example.

Answer: Air contains nitrogen (about 78%), oxygen (about 21%), carbon dioxide, argon and other gases (together about 1%), along with water vapour and dust particles.

Teacher's Note:
1. Write the gases in order of quantity.
2. Water vapour and dust vary from place to place.

Answer: Gases have a lot of empty space between their particles. When pressure is applied, the particles are pushed closer, so air can be compressed.

Teacher's Note:
1. This is why a bicycle pump can force air into a tyre.
2. Liquids and solids have little space between particles.

Answer: Hold a glass bottle upside down and push it straight down into a bucket of water. Water does not fill the bottle fully, and bubbles escape when the bottle is tilted. This shows that the bottle was full of air, which occupies space.

Teacher's Note:
1. Keep the bottle straight while pushing it in.
2. Air bubbles are the visible proof.

Answer: Fill a glass with ice-cold water and keep it in the open for some time. Droplets of water form on the outer surface of the glass. The water vapour present in the air cools on touching the cold glass and condenses into droplets.

Teacher's Note:
1. The water does not leak out of the glass.
2. Condensation shows that vapour is present in air.

Answer: 1. Living things breathe the oxygen in air.
2. Plants use carbon dioxide in air to make food.
3. Oxygen in air helps fuels burn.
4. Moving air (wind) turns windmills and dries clothes.
5. Air is used to fill tyres and balloons, and birds and aeroplanes use it to fly.

Teacher's Note:
1. Any five correct uses are acceptable.
2. Write short, clear points.

Answer: Light a candle and cover it with an inverted glass jar. After a short time the flame becomes dim and goes out. The oxygen inside the closed jar has been used up, which shows that air (oxygen) is needed for burning.

Teacher's Note:
1. Compare with an uncovered candle, which keeps burning.
2. Oxygen is the part of air that supports burning.

Answer: At great heights the air is thin and has less oxygen, and under water there is no air to breathe. So they carry cylinders to get enough oxygen for breathing.

Teacher's Note:
1. Divers also use cylinders with a mixture of gases for safety.
2. Both situations lack easily available oxygen.

Answer: Smoke from vehicles and factories, dust, burning of wood, coal and garbage, and harmful gases such as carbon monoxide and sulphur dioxide make air impure. Natural events like volcanic eruptions and forest fires also add smoke and ash.

Teacher's Note:
1. Substances that spoil the air are called pollutants.
2. Most pollutants come from human activities.

Answer: Gases like carbon dioxide and methane in the atmosphere trap some of the heat from the Sun, which keeps the Earth warm enough for life. This natural heat-trapping is called the greenhouse effect.

Teacher's Note:
1. Without it, the Earth would be too cold for most living things.
2. Problems begin when too much of these gases is added.

Answer: Global warming is the gradual rise in the average temperature of the Earth. It happens because burning fuels and cutting forests increase the greenhouse gases in the air, so more heat is trapped.

Teacher's Note:
1. Melting ice and rising sea levels are its effects.
2. Planting trees helps to reduce it.

Answer: 1. Use public transport, cycling or walking instead of private vehicles.
2. Use cleaner fuels such as CNG and solar energy.
3. Plant more trees.
4. Do not burn garbage, crop residue or leaves.
5. Keep vehicles and factory chimneys well maintained.

Teacher's Note:
1. Even small daily habits help.
2. Trees take in carbon dioxide and release oxygen.

Answer: The candle burns for a short time and then goes out, and the water rises in the jar by about one-fifth of its height. The burning candle used up the oxygen, which is about one-fifth of air. So air contains oxygen, which supports burning.

Teacher's Note:
1. The water rises to fill the space left by the oxygen used.
2. The remaining gas, mainly nitrogen, does not support burning.

Answer: No. Only oxygen supports burning and is used up by the candle. Nitrogen and the other gases do not burn or support burning, so the water would not rise for them.

Teacher's Note:
1. This is why only about one-fifth of the jar fills with water.
2. Other gases stay in the jar unchanged.