GSEB Class 11 Chemistry Solutions Chapter 14 Environmental Chemistry

Question 1. Define environmental chemistry.
Answer: Environmental chemistry is concerned with understanding the origin, movement, reactions, impacts, and final states of chemical substances in our surroundings.
In simple words: Environmental chemistry looks at how chemicals start, travel, change, affect things, and end up in the natural world.

Exam Tip: When defining a scientific term, always include its scope, key processes, and the subject it studies for a complete answer.

Question 2. Explain tropospheric pollution in 100 words.
Answer: Tropospheric pollution happens because of harmful solid or gaseous particles in the air. The lower layer of Earth's atmosphere, called the troposphere, contains many primary gaseous and particulate pollutants. These include:
1. Gaseous air pollutants: These are compounds like sulfur oxides, nitrogen and carbon oxides, hydrogen sulfide, various hydrocarbons, ozone, and other reactive oxidants.
2. Particulate pollutants: These are tiny solid or liquid particles such as dust, mist, fumes, smoke, and smog.
Let's look at some major gaseous air pollutants in more detail:
(a) Oxides of sulfur: These are formed when sulfur-containing fossil fuels are burned. Sulfur dioxide \( (\text{SO}_2) \) gas is harmful to both animals and plants.
(b) Oxides of Nitrogen: Dinitrogen \( (\text{N}_2) \) and dioxygen \( (\text{O}_2) \) are main gases in the air. At high altitudes, lightning causes them to react and form nitrogen oxides.
\( \text{N}_2(\text{g}) + \text{O}_2(\text{g}) \xrightarrow{\text{1483K}} \text{2NO}(\text{g}) \)
\( \text{2NO}(\text{g}) + \text{O}_2(\text{g}) \rightarrow \text{2NO}_2(\text{g}) \)
\( \text{NO}(\text{g}) + \text{O}_3(\text{g}) \rightarrow \text{NO}_2(\text{g}) + \text{O}_2(\text{g}) \)
(c) Hydrocarbons: These come from the incomplete burning of fuel in vehicles and can cause cancer.
(d) Oxides of carbon: Carbon monoxide \( (\text{CO}) \) is a very serious air pollutant, mostly released from burning coal, firewood, or petrol without enough oxygen. Carbon dioxide \( (\text{CO}_2) \) is also released into the air by breathing, burning fossil fuels, volcanic eruptions, and cement factories.
In simple words: Tropospheric pollution is caused by unwanted solid or gas particles in the air. Key gases are sulfur, nitrogen, and carbon oxides, hydrocarbons, and ozone. Tiny particles like dust and smoke also contribute. These come from burning fuels and natural events, leading to harmful effects.

Exam Tip: When explaining a complex topic like pollution, break it down into categories (e.g., gaseous, particulate) and provide specific examples for each to make your answer clear and comprehensive.

Question 3. Carbon monoxide gas is more dangerous than carbon dioxide gas. Why?
Answer: The presence of carbon monoxide \( (\text{CO}) \) reduces the amount of hemoglobin in red blood cells \( (\text{RBCs}) \) by binding with it about 300 times more easily than oxygen. This forms carboxyhemoglobin, a stable compound, as shown below:
\( \text{CO} + \text{Hb} \rightleftharpoons \text{HbCO} \)
Because of this, hemoglobin cannot join with oxygen to create oxyhemoglobin and transport oxygen to different body cells. Carbon monoxide is so toxic that a concentration of 1300 ppm in the air can be fatal within half an hour.
In simple words: Carbon monoxide is dangerous because it sticks to our blood's oxygen carrier, hemoglobin, much more strongly than oxygen does. This stops oxygen from getting to our body's cells, which can be deadly.

Exam Tip: To explain why one substance is more dangerous than another, describe the specific mechanism of harm and provide quantitative comparisons if possible, like the binding affinity example here.

Question 4. List gases which are responsible for greenhouse effect?
Answer: Carbon dioxide \( (\text{CO}_2) \) is the main contributor to global warming or the greenhouse effect. Other gases that also contribute include methane \( (\text{CH}_4) \), ozone \( (\text{O}_3) \), chlorofluorocarbon compounds \( (\text{CFCs}) \), nitrogen oxides, and water vapor. These gases trap heat in the atmosphere, leading to global warming.
In simple words: Carbon dioxide is the biggest cause of the greenhouse effect. Other gases like methane, ozone, CFCs, nitrogen oxides, and water vapor also contribute by trapping heat in the atmosphere, causing the Earth to warm up.

Exam Tip: When listing greenhouse gases, remember to include both the common names and their chemical formulas for accuracy.

Question 5. Statues and monuments in India are affected by acid rain. How?
Answer: Acid rain is rainwater that contains sulfuric acid and nitric acid, along with a small amount of hydrochloric acid, and has a pH of 4-5. Acid rain severely harms statues and monuments, especially those made of marble, limestone, slate, or mortar. For example, the Taj Mahal in Agra, which is made of marble \( (\text{CaCO}_3) \), is being damaged by acid rain. The reaction is:
\( \text{CaCO}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{CaSO}_4 + \text{CO}_2 + \text{H}_2\text{O} \)
As a result, the marble corrodes and wears away, causing pits and discoloration, which makes it lose its shine.
In simple words: Acid rain, which contains acids, harms statues and monuments. It specifically damages marble, causing it to wear away, get holes, and lose its bright color, as seen with the Taj Mahal.

Exam Tip: When explaining the effect of acid rain, always mention the chemical compounds involved, the pH range, and give a specific example with the relevant chemical reaction.

Question 6. What is smog? How is classical smog different from photochemical smogs?
Answer: The word 'smog' comes from combining 'smoke' and 'fog'. It is a well-known example of air pollution that happens in many cities globally. There are two main kinds of smog:
(a) Classical smog forms in cool, damp weather. It is a mix of smoke, fog, and sulfur dioxide. Chemically, it is a reducing mixture, so it is also known as reducing smog.
(b) Photochemical smog happens in warm, dry, and sunny conditions. The main parts of photochemical smog result from sunlight acting on unsaturated hydrocarbons and nitrogen oxides produced by cars and factories. Photochemical smog contains a high level of oxidizing agents, and therefore, it is also called oxidizing smog.
In simple words: Smog is a mix of smoke and fog, a common type of air pollution. Classical smog forms in cold, wet weather from smoke, fog, and sulfur dioxide. Photochemical smog forms in warm, sunny weather from car and factory emissions reacting with sunlight.

Exam Tip: Clearly differentiate between classical and photochemical smog by mentioning the climate conditions, primary components, and whether they are reducing or oxidizing in nature.

Question 7. Write down the reactions involved during the formation of photochemical smog.
Answer: When fossil fuels are burned, many pollutants are released into the Earth's lower atmosphere (troposphere). Two of these pollutants are hydrocarbons (unburned fuels) and nitric oxide \( (\text{NO}) \). When these pollutants build up to high levels, a chain reaction happens with sunlight, turning \( \text{NO} \) into nitrogen dioxide \( (\text{NO}_2) \). This \( \text{NO}_2 \) takes in energy from sunlight and breaks apart into nitric oxide and a free oxygen atom.
\( \text{NO}_2(\text{g}) \xrightarrow{h\nu} \text{NO}(\text{g}) + \text{O}(\text{g}) \) ... (i)
Oxygen atoms are very reactive and can combine with the \( \text{O}_2 \) in the air to make ozone.
\( \text{O}(\text{g}) + \text{O}_2(\text{g}) \rightarrow \text{O}_3(\text{g}) \) ... (ii)
The ozone formed in the above reaction (ii) quickly reacts with the \( \text{NO}(\text{g}) \) made in reaction (i) to remake \( \text{NO}_2 \). \( \text{NO}_2 \) is a brown gas and at high levels can cause haze.
\( \text{NO}(\text{g}) + \text{O}_3(\text{g}) \rightarrow \text{NO}_2(\text{g}) + \text{O}_2(\text{g}) \) ... (iii)
Ozone is a toxic gas, and both \( \text{NO}_2 \) and \( \text{O}_3 \) are strong oxidizing agents. They can react with the unburnt hydrocarbons in the polluted air to create chemicals like formaldehyde \( (\text{HCHO}) \), acrolein \( (\text{CH}_2 = \text{CH CHO}) \), and peroxyacetyl nitrate \( (\text{PAN}) \).
\( \text{3CH}_4 + \text{2O}_3 \rightarrow \text{3HCHO} + \text{3H}_2\text{O} \)
Formaldehyde: \( \text{HCHO} \)
Acrolein: \( \text{CH}_2 = \text{CHCHO} \)
Peroxyacetyl nitrate (PAN): \( \text{CH}_3\text{CO}_3\text{NO}_2 \)
In simple words: Photochemical smog starts when car and factory fumes (hydrocarbons and nitric oxide) mix with sunlight. This creates nitrogen dioxide, which breaks down to form ozone. Both ozone and nitrogen dioxide react with other pollutants to make harmful chemicals like formaldehyde, acrolein, and PAN.

Exam Tip: When asked for reactions, provide all relevant chemical equations clearly, ensuring reactants and products are balanced and conditions (like \( h\nu \) for light) are indicated.

Question 8. What are the harmful effects of photochemical smog and how can they be controlled?
Answer: Photochemical smog, which consists of ozone \( (\text{O}_3) \), nitric oxide \( (\text{NO}) \), acrolein \( (\text{CH}_2 = \text{CH CHO}) \), formaldehyde \( (\text{HCHO}) \), and peroxyacetyl nitrate \( (\text{PAN}) \), causes serious health problems. Both \( \text{O}_3 \) and \( \text{PAN} \) are powerful eye irritants. \( \text{O}_3 \) and \( \text{NO} \) irritate the nose and throat, and high concentrations of these gases can cause headaches, chest pain, a dry throat, coughing, and breathing difficulties. Photochemical smog also causes rubber to crack and extensively damages plant life. It also causes corrosion of metals, stones, building materials, rubber, and painted surfaces.
**Control of photochemical smog:** Many methods are used to prevent or lessen the creation of photochemical smog. If the main precursors \( (\text{NO}_2 \) and hydrocarbons) of photochemical smog are controlled, secondary precursors such as \( \text{O}_3 \) and \( \text{PAN} \) will automatically decrease. Catalytic converters are commonly used in cars to stop the release of \( \text{NO} \) and unburnt hydrocarbons into the air. Certain plants, such as Pinus, Juniparus, Quercus, Pyrus, and Vitis, can absorb \( \text{NO} \), and planting them can help control the formation of photochemical smog.
In simple words: Photochemical smog, made of gases like ozone and PAN, hurts our health by irritating eyes, nose, and throat, causing breathing issues. It also damages rubber, plants, and materials. To control it, we can reduce car and factory emissions using catalytic converters and plant specific trees that absorb nitric oxide.

Exam Tip: For questions about effects and control, list specific harmful impacts (e.g., eye irritation, material damage) and provide practical control methods (e.g., catalytic converters, specific plants).

Question 9. What are the reactions involved for ozone layer depletion in the stratosphere?
Answer: The upper part of the atmosphere, called the stratosphere, contains a significant amount of ozone \( (\text{O}_3) \), which shields us from harmful UV radiation \( (\lambda = 255 \text{ nm}) \) from the sun. Recently, reports have shown a thinning of this protective ozone layer. The main reason for this ozone depletion is thought to be the release of chlorofluorocarbon compounds \( (\text{CFCs}) \), also known as freons. These are widely used in refrigerators and air conditioners because they are unreactive, non-flammable, and non-toxic organic molecules.
When \( \text{CFCs} \) are released into the atmosphere, they mix with normal atmospheric gases and eventually reach the stratosphere. In the stratosphere, powerful UV radiation breaks them down, releasing a free chlorine radical.
\( \text{CF}_2\text{Cl}_2(\text{g}) \xrightarrow{h\nu} \cdot\text{Cl}(\text{g}) + \cdot\text{CF}_2\text{Cl}(\text{g}) \)
The chlorine free radical then reacts with stratospheric ozone to form chlorine monoxide radicals \( (\text{ClO}) \) and molecular \( \text{O}_2 \).
\( \cdot\text{Cl} + \text{O}_3(\text{g}) \rightarrow \text{ClO}\cdot(\text{g}) + \text{O}_2(\text{g}) \)
The \( \text{ClO} \) radical reacts with atomic oxygen, releasing more \( \cdot\text{Cl} \) radicals:
\( \text{ClO}\cdot + \text{O}(\text{g}) \rightarrow \cdot\text{Cl}(\text{g}) + \text{O}_2(\text{g}) \)
These chlorine radicals are constantly recreated and cause ozone to break down. Thus, \( \text{CFCs} \) act as carriers that continuously generate chlorine radicals in the stratosphere, damaging the ozone layer and causing its depletion.
In simple words: Ozone depletion happens when chemicals called CFCs reach the upper atmosphere. UV light breaks CFCs apart, releasing chlorine. This chlorine then breaks down ozone molecules repeatedly, creating a "hole" in the protective ozone layer.

Exam Tip: Focus on the role of CFCs as a source of chlorine radicals and the chain reactions that show how these radicals continuously break down ozone molecules, highlighting the catalytic nature of the process.

Question 10. What do you mean by ozone hole? What are its consequences?
Answer: In the 1980s, scientists studying the atmosphere in Antarctica observed a thinning of the ozone layer, commonly known as the ozone hole, over the South Pole. This depletion of the ozone shield, or ozone hole, has dangerous outcomes. It will permit more UV radiation to pass through into the stratosphere without being blocked. UV radiation causes skin lesions, cataracts, sunburn, skin cancer, and the death of many tiny marine plants (microphytoplanktons), and harms fish productivity. Plant proteins are easily affected by UV radiation, leading to harmful changes in cells.
It also increases the evaporation of surface water through the pores (stomata) of leaves and decreases the soil's moisture content. Increased UV radiation damages paints and fibers, causing them to fade faster.
In simple words: The "ozone hole" is a thinning of the ozone layer, first seen over Antarctica. This lets in more harmful UV radiation from the sun. The consequences include higher risks of skin cancer and cataracts, harm to tiny sea plants and fish, damage to plant cells, and faster fading of paints and fabrics.

Exam Tip: Define the ozone hole by its location and impact, then clearly list its consequences, categorizing them by affected areas like human health, marine life, plants, and materials.

Question 11. What are the major causes of water pollution? Explain.
Answer: Water pollution mostly comes from human activities. The main reasons for water pollution are:
(i) Pathogens: The most serious water pollutants are disease-causing agents called pathogens. Pathogens include bacteria and other tiny organisms that get into water from household sewage and animal waste. Human waste contains bacteria such as Escherichia coli and Streptococcus faecalis, which cause stomach and gut problems.
(ii) Organic waste: Another major water pollutant is organic matter like leaves, grass, and garbage. A large number of bacteria break down this organic matter in the water. The amount of oxygen water can hold is used up by these bacteria. The amount of dissolved oxygen in water is very important for water animals and plants.
When there isn't enough oxygen in the water, aquatic life that needs oxygen dies. Then, anaerobic bacteria (which don't need oxygen) start to break down the organic waste, producing chemicals that smell bad and are harmful to people. Aerobic (oxygen-requiring) bacteria break down these organic wastes and keep the water low in dissolved oxygen.
(iii) Chemical pollutants: Water is an excellent solvent and dissolves inorganic chemicals that include heavy metals like cadmium, mercury, and nickel, which form an important group of pollutants. These chemicals are extremely dangerous to humans because our bodies cannot remove them. Organic chemicals from petroleum products pollute many water sources, for example, large oil spills in the ocean.
Various industrial waste materials like polychlorinated biphenyls \( (\text{PCBs}) \) used as cleaning solvents, detergents, and fertilizers also add to water pollution. Algae grow a lot due to the phosphates in fertilizers. These large algae growths often release toxins into the water.
In simple words: Water pollution mainly comes from people. Major causes include pathogens (disease-causing germs from waste), organic waste (like leaves and trash that use up oxygen in water), and chemical pollutants (heavy metals and industrial waste like PCBs and fertilizers that cause algae blooms and toxins).

Exam Tip: When explaining causes of pollution, categorize them (e.g., pathogens, organic waste, chemical pollutants) and provide a brief explanation for each category, including specific examples and their impact.

Question 12. Have you ever observed any water pollution in your area? What measures would you suggest to control it?
Answer: Yes, I have observed water pollution in my area, mainly from industrial effluents and domestic sewage flowing into local rivers. To control it, several measures can be suggested:
Industrial waste from paper, textile, and chemical factories should not be allowed to mix with water bodies like rivers.
Non-biodegradable detergents should be avoided, and only biodegradable detergents and soaps should be used for washing or bathing.
The pH of water should be checked regularly. Pure water has a pH of 7. If its pH is below 7, it means it contains acidic impurities like dissolved sulfur dioxide \( (\text{SO}_2) \) or hydrogen sulfide \( (\text{H}_2\text{S}) \). If its pH is above 7, it means it contains basic impurities like detergents. Any abnormal pH should be immediately reported to the local Pollution Control Board so action can be taken to control pollution in rivers, ponds, streams, or lakes.
In gardens, use compost instead of chemical fertilizers. Avoid using DDT malathion at home and try to use dried neem leaves to keep insects away. Adding a crystal of potassium permanganate \( (\text{KMnO}_4) \) or bleaching powder or alum to the house water tank can help purify the water.
In simple words: Yes, I have seen water pollution. To fix it, factories should not dump waste into rivers, and people should use eco-friendly soaps. We need to check water pH and report pollution to authorities. For homes and gardens, use natural fertilizers like compost instead of chemicals, and natural insect repellents like neem leaves. Adding potassium permanganate or alum to water tanks can also help.

Exam Tip: When suggesting control measures, provide a range of solutions, including policy-level actions (industrial regulations), individual actions (detergent choice), and community-level monitoring (pH checks, reporting to authorities).

Question 13. What do you mean by Biochemical oxygen demand (BOD)?
Answer: Biochemical Oxygen Demand \( (\text{BOD}) \): This refers to the amount of oxygen that bacteria require to break down the organic matter present in a specific volume of a water sample. The \( \text{BOD} \) in water shows how much organic material is present in it, in terms of how much oxygen will be needed to break it down naturally. Clean water would typically have a \( \text{BOD} \) value of 17 ppm or less.
In simple words: BOD is a measure of how much oxygen bacteria need to break down all the organic waste in a water sample. It tells us how much organic pollution is in the water; lower BOD means cleaner water.

Exam Tip: Clearly define BOD, explain what it measures (oxygen required for organic matter breakdown), and state the significance of its value (indicator of water purity).

Question 14. Do you observe any soil pollution in your neighbourhood? What efforts will you make for controlling the soil pollution?
Answer: Yes, I do observe soil pollution in my neighborhood, mainly from the excessive use of insecticides and pesticides in gardens and agricultural fields. Herbicides also cause soil pollution. Thus, these chemicals need to be used carefully. In the past (and even now), DDT was used to control damage from insects, rodents, weeds, and various crop diseases. Pesticides are essentially synthetic toxic chemicals with serious environmental impacts.
Later, other organic toxins like Aldrin and Dieldrin were introduced. Most of these toxins do not dissolve in water and do not break down naturally. This causes severe metabolic and physiological issues in animals. Nowadays, herbicides such as sodium chlorate \( (\text{NaClO}_3) \) and sodium arsenite \( (\text{Na}_3\text{AsO}_3) \) are used. Even these are not good for the environment.
**Efforts for controlling soil pollution:**
Controlling and managing such pollution-causing substances is very important. Household waste should be collected in two separate bins: one for biodegradable materials like food and vegetable waste, and another for non-biodegradable items like plastics, toys, and cans. Biodegradable waste is put in landfills, while non-biodegradable waste should be recycled.
The use of synthetic fertilizers, pesticides, insecticides, and herbicides should be minimized. Proper management is needed not only for domestic waste but also for medical, agricultural, industrial, and mining waste. Polythene bags should be avoided and not allowed to mix with animal fodder.
In simple words: Yes, I see soil pollution from too many insecticides and pesticides. To control it, we should use fewer chemicals, separate biodegradable from non-biodegradable trash, recycle, and avoid polythene bags. Also, better waste management for all types of waste is crucial.

Exam Tip: For questions asking for observation and control, start by stating your observation, then detail the causes, and finally, list specific, actionable control measures covering different types of waste and pollutants.

Question 15. What are pesticides and herbicides? Explain giving examples.
Answer:
**Pesticides:** Pesticides are essentially artificial toxic chemicals with environmental effects. Earlier, DDT [2, 2-(bis-p-chlorophenyl)-1, 1, 1-trichloroethane] was used to control insect-borne diseases in crops. Later, as insects became resistant to DDT, other organic toxins like Aldrin and Dieldrin were used as pesticides. Most organic toxins are water-insoluble and do not break down naturally. More recently, biodegradable products called organo-phosphates and carbamates have been introduced. However, these are strong nerve toxins and thus more harmful to people. There have been several pesticide-related deaths among farm workers.
**Herbicides:** Herbicides include chemicals like sodium chlorate \( (\text{NaClO}_3) \) and sodium arsenite \( (\text{Na}_3\text{AsO}_3) \). Most herbicides are toxic to mammals but do not last as long as organochlorides. These chemicals break down within a few months. Like organochlorides, these two become concentrated in the food chain. Some herbicides can cause birth defects. Studies show that cornfields sprayed with herbicides are more prone to insect attacks than fields that are weeded by hand.
In simple words: Pesticides are toxic chemicals used to kill pests, like DDT or Aldrin, but they can be very harmful to the environment and people. Herbicides are chemicals like sodium chlorate used to kill weeds, which are also toxic but usually break down faster than some pesticides.

Exam Tip: When defining pesticides and herbicides, include their primary purpose, examples of specific chemicals, and mention their environmental and health implications for a comprehensive answer.

Question 16. What do you mean by green chemistry? How will it help decrease environmental pollution?
Answer: Green chemistry is a way of thinking that involves using current knowledge and principles of chemistry and other sciences to reduce the negative impact of pollution on the environment. Green chemistry is a production approach that aims to cause the least pollution or damage to the environment.
Byproducts created during a process, if not used productively, add to environmental pollution. Such processes are not only bad for the environment but also wasteful. Both waste generation and its disposal are financially inefficient. Using current knowledge to reduce chemical hazards along with development activities is the basis of green chemistry. This approach aims to design chemical products and processes that minimize the use and generation of hazardous substances, thereby helping to lessen environmental pollution.
In simple words: Green chemistry uses chemical principles to make products and processes that create less pollution and are safer for the environment. It helps by making sure less waste is produced and that any waste is less harmful, reducing overall environmental damage.

Exam Tip: When defining green chemistry, emphasize its core principle of reducing environmental impact through chemical design, and then explain *how* it achieves this (e.g., minimizing hazardous substances, reducing waste).

Question 17. What would have happened if the greenhouse gases were totally missing in the earth's atmosphere? Discuss.
Answer: The main gases responsible for the greenhouse effect are carbon dioxide, methane, water vapor, nitrous oxide, CFCs, and ozone. These gases trap heat, keeping the Earth warm enough to support life.
If greenhouse gases were completely absent from Earth's atmosphere, the planet would be much colder, similar to Mars. Without the natural greenhouse effect, the Earth's average temperature would drop significantly, likely becoming too cold for liquid water to exist widely and thus unable to support most forms of life as we know it. The delicate balance of Earth's climate relies on the presence of these gases to maintain a habitable temperature. Their absence would lead to an uninhabitable, frozen world.
In simple words: If there were no greenhouse gases, Earth would be extremely cold, like Mars. The temperature would drop so much that liquid water wouldn't exist, making it impossible for most life to survive. Greenhouse gases are crucial for keeping our planet warm enough to live on.

Exam Tip: To answer a hypothetical "what if" question, first state the primary role of the elements in question (greenhouse gases in this case), then describe the dramatic and specific consequences of their complete absence.

Question 18. A large number of fish are suddenly found floating dead on a lake. There is no evidence of toxic dumping but you find an abundance of phytoplankton. Suggest a reason for the fish kill.
Answer: The excessive growth of phytoplankton in the lake's water is a cause of water pollution. Although phytoplankton are biodegradable, their large population means a large number of bacteria will decompose this organic matter in the water. The amount of oxygen that water can hold is limited. In cold water, dissolved oxygen \( (\text{DO}) \) can reach concentrations up to 10 ppm. Even a moderate amount of organic matter, when broken down by bacteria in water, can reduce the water's dissolved oxygen. When the low concentration of dissolved oxygen, which was enough to support aquatic life, is used up, the fish die from lack of oxygen.
In simple words: A lot of dead fish, with lots of phytoplankton and no toxic dumping, suggests oxygen depletion. Many phytoplankton mean many bacteria breaking them down, which uses up all the oxygen in the water. Without oxygen, fish cannot breathe and die.

Exam Tip: When explaining ecological phenomena, connect the observed facts (phytoplankton abundance) to a clear causal chain (decomposition, oxygen depletion, fish kill) for a logical explanation.

Question 19. How can domestic waste be used as manure?
Answer: Domestic waste can be used as manure by separating it into different types. Waste is collected in two small bins, A and B. Bin A, which is green, contains biodegradable materials like food scraps, vegetable leaves, fruit skins, and seeds. Bin B contains non-biodegradable items such as plastics, broken toys, cans, and plastic bottles. The contents of Bin B are sent for recycling. In contrast, Bin A's biodegradable material is sent through local agencies for landfilling, where it naturally breaks down and converts into manure (compost).
In simple words: Domestic waste can become manure by sorting it. Biodegradable items like food scraps go into one bin and are sent to landfills to decompose into compost. Non-biodegradable items go into another bin for recycling.

Exam Tip: When describing waste management, explain the importance of segregation (biodegradable vs. non-biodegradable) and the specific fate of each type, focusing on the conversion of organic waste into useful manure.

Question 20. For your agriculture field or garden, you have developed a compost producing pit. Discuss the process in the light of bad odour, flies and recycling of wastes for wastes for a good produce.
Answer: Domestic waste is categorized into two types: biodegradable and non-biodegradable. Non-biodegradable waste, like plastic, glass, and metal scraps, is sent for recycling. Biodegradable waste, even though it can produce a foul smell and attract many flies if left open, is a nuisance that can cause water pollution and sewage issues. To manage this, the biodegradable waste is mechanically broken into smaller pieces and placed in a pit, then covered with a thin layer of sand in one corner. Due to bacterial action and the heat generated during decomposition, it slowly transforms into compost, which is an organic manure suitable for use in agricultural fields or gardens.
In simple words: In a compost pit, biodegradable waste is broken down by bacteria into manure. To handle bad smells and flies, the waste is shredded and covered with sand. This process helps recycle waste into valuable plant food for gardens and fields.

Exam Tip: When discussing composting, explain the process (segregation, breakdown), address common problems like odor and flies, and highlight the benefit of recycling waste into a useful product like manure.