Frank Brothers Solutions for ICSE Class 9 Chemistry Chapter 10 Atmospheric Pollution

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Question 1:
Answer: Acid rain is the rain that has an excessive amount of acid in it than that of normal. Two air pollutants that cause acid rain are 1. Oxides of nitrogen 2. Oxides of sulphur.
Acid rain forms when these gases mix with water vapor in the air to create acidic droplets. It doesn't look different from normal rain but has a much lower pH level.
Teacher's Tip: Remember the "Big Two" culprits of acid rain: Nitrogen and Sulphur.
Exam Tip: Always mention the full chemical names (Oxides of Nitrogen/Sulphur) rather than just the single elements.

Question 2:
Answer: Acid rain is responsible for retarding forest’s growth and other vegetation. Acid rain makes the soil acidic and adversely affects the plants.
When soil becomes too acidic, it leaches away vital minerals that trees need to survive. This weakens the plants, making them more likely to die from disease or cold weather.
Teacher's Tip: Think of acid rain as "sour rain" that makes the ground too tart for plants to grow properly.
Exam Tip: Use the scientific word "retards" to describe the slowing of growth for more precise marks.

Question 3:
Answer: 70% of acid rain is due to sulphur dioxide. Oxides of sulphur and nitrogen released into atmosphere from number of sources. These oxides of nitrogen gets converted into nitrogen dioxide(NO₂) which reacts with water to form nitric acid. Similarly, sulphur dioxide reacts with atmospheric oxygen to form sulphur trioxide which with water forms sulphuric acid. These come down on earth as acid rain.
High-temperature combustion in factories and cars is the primary source of these precursor gases. Once in the clouds, they undergo a chemical transformation into liquid acids that can travel for miles.
Teacher's Tip: Sulphur Dioxide (SO₂) is the "Heavyweight Champion" causing the majority of acid rain.
Exam Tip: Mentioning that SO₂ accounts for 70\% of the damage shows you have studied specific statistics.

Question 4:
Answer: Acid rain can be reduced by 1. There should be reduction in fossil fuel combustion. 2. Use of alternate cleaner energy sources should be encouraged. Eg-nuclear power, hydro power, wind energy, solar energy etc. 3. Air filters and scrubbers are fitted in tall industrial chimneys to control air pollution. 4. Catalytic converters in vehicle reduce nitrogen oxide emissions from automobiles.
Transitioning to solar or wind power stops the pollutants from entering the atmosphere in the first place. For existing factories, scrubbers act like giant vacuum cleaners that wash the smoke before it leaves the chimney.
Teacher's Tip: Think of "Scrubbers" like a bar of soap for cleaning industrial smoke.
Exam Tip: Listing specific clean energy alternatives like "solar" or "wind" makes your answer much stronger.

Question 5:
Answer: Acid rain cause extensive damage to the environment.
1. Vegetation - The acid rain makes the soil acidic. This adversely affects the plants and animals. This damages leaves of plants and trees. This is responsible for retarding forests and other vegetation.
2. Fertility of soil - The activity of symbiotic nitrogen fixing bacteria present in the nodules of leguminous family is inhibited. This is responsible for destroying or reducing the fertility of the soil.
3. Water bodies - Acid rain renders the river, lakes or even ocean water acidic, there by adversely affecting marine animals. Changes in pH affect the reproduction and survival of many species of fish and other animals.
4. Buildings and monuments - Acid rain cause extensive damage to the buildings and monuments made from marbles, limestone, slate and mortar.
CaCO₃ + H₂SO₄ →CaSO₄ + H₂O + CO₂
Calcium Calcium sulphate
Acid rain can literally dissolve the surface of famous marble statues, turning detailed carvings into smooth stone. In lakes, it can kill fish eggs, leading to a total collapse of the local food chain.
Teacher's Tip: Use the word "leaching" when talking about soil minerals and "corrosion" when talking about monuments.
Exam Tip: Memorize the CaCO₃ equation; it is a favorite for gaining extra "short answer" marks.

Question 6:
Answer: 5. Ecological balance - Acid rain is responsible for wiping out many bacterial and blue green algae, so disrupting the whole ecological balance.
6. Human health - Acid rain has been found to be dangerous to human health. Acidic conditions can affect human nervous, respiratory and digestive systems.
When the tiny organisms at the bottom of the food chain die, the entire ecosystem loses its balance. For humans, breathing in the fine particles associated with acid rain can lead to asthma and bronchitis.
Teacher's Tip: Pollution is a "Chain Reaction" – what hurts the smallest algae eventually hurts the whole lake.
Exam Tip: Mention "respiratory" health specifically when discussing the impacts of air-related pollution.

Question 6 (Continued):
Answer: Air pollution is a harmful change in the natural air quality. It includes all physical, chemical and biological agents that modify the natural characteristics of the atmosphere.
Air pollution changes the air we breathe by adding substances that shouldn't be there. These agents can be visible like smoke or invisible like toxic gases.
Teacher's Tip: Think of air pollution as anything that "spoils" the clean recipe of our atmosphere.
Exam Tip: Define air pollution as a "harmful change" to cover all types of biological and chemical agents.

Question 7:
Answer: Ozone is an allotrope of oxygen. It has three oxygen atoms and its molecular formula is O3 It is an unstable blue gas having pungent odour found in troposphere. It is used as a powerful oxidant, bleach and water purifier.
Ozone is a double-edged sword; it is a lifesaver high in the atmosphere but a toxic pollutant near the ground. It is composed of three oxygen atoms bonded together, unlike the oxygen we breathe which has only two.
Teacher's Tip: Just remember: O₂ is for breathing, O₃ is for shielding!
Exam Tip: Use the scientific term "allotrope" to describe the relationship between oxygen and ozone.

Question 8:
Answer: The gases causing ozone depletion are 1. Chlorofluoro carbons(CFCs or freons) 2. Methane 3. Nitrous oxides 4. Carbon tetrachloride 5. Methyl bromide(a soil fumigant and insecticide) 6. Aircraft emission 7. n-propyl bromide and Halon-1202.
Many of these chemicals were used in old refrigerators before scientists realized they were eating the atmosphere. These stable compounds travel high up and break apart ozone molecules through fast chemical reactions.
Teacher's Tip: CFCs are the "Ozone Eaters" – they are the biggest threat to our protective shield.
Exam Tip: Be sure to mention CFCs first as they are the most significant cause of ozone layer depletion.

Question 9:
Answer: Greenhouse gases are 1. Water vapour(H₂O) 2. Carbon dioxide(CO₂) 3. Methane(CH₄) 4. Oxides of nitrogen(NO_x).
These gases act like a thermal blanket, allowing sunlight to pass through but trapping the resulting heat inside. While some greenhouse effect is natural, human activities have increased their concentration to dangerous levels.
Teacher's Tip: Think of Greenhouse gases as the "Glass Walls" of Earth's heat trap.
Exam Tip: Don't forget that water vapour (H₂O) is actually a very important natural greenhouse gas.

Question 10:
Answer: Ozone layer is formed in stratosphere when oxygen molecules photo dissociate after absorbing an UV photon of shorter wavelength (less than 240{ nm}) to produce two oxygen atoms.
O₂ →{UV Radiation} O + O { or } 1/2 O₂ + 1/2 O₂
O + O₂ →O₃
Ozone
High-energy UV light from the sun provides the energy needed to split oxygen molecules into individual atoms. This process is a continuous cycle that naturally creates and destroys ozone in the upper atmosphere.
Teacher's Tip: The Sun is both the "creator" of ozone and the reason we need its protection!
Exam Tip: Write the chemical reactions in two clear steps to show exactly how ozone is created.

Question 11:
Answer: Greenhouse effect means the progressive warming up of the earth’s surface due to the blanketing effect of man made carbon dioxide in the atmosphere. Greenhouse is a glasshouse with plants inside and which allows short wave, incoming solar radiation to come in but does not allow the long wave, i.e. outgoing infrared radiation to escape from inside the structure. Some of the gases in the earth’s atmosphere act like the glass in a greenhouse. They trap sun’s heat and keep the surface of the earth warm. Carbon dioxide and water vapour act as a greenhouse.
Sunlight enters as short waves which the earth absorbs and re-emits as long infrared waves. Greenhouse gases are opaque to these longer waves, bouncing them back toward the surface and raising the temperature.
Teacher's Tip: It is like a car parked in the sun with the windows rolled up – it gets much hotter inside than outside!
Exam Tip: Explain the difference between "short-wave" incoming radiation and "long-wave" outgoing radiation.

Question 12:
Answer: Global warming is rise in the average global earth temperature. An increase in the average temperature of the earth’s atmosphere due to greenhouse effect which can have far reaching effects on the climate and consequently on the key life, support systems of the planet, and this phenomenon is called global warming.
Even a small increase of one or two degrees in the global average can lead to massive changes in weather patterns. This is not just about "hot weather" but about the entire planet's climate system shifting.
Teacher's Tip: Global Warming is the "Symptom" and the Greenhouse Effect is the "Cause."
Exam Tip: Define Global Warming specifically as the "average" rise in temperature across the whole planet.

Question 13:
Answer: [Fig 10.1: Greenhouse effect. Image shows SUN radiating light. Light from Sun enters the atmosphere. Some heat from earth radiates back in to space. Layer of CO2 traps some heat. Some heat reflected back to earth (Green house effect)]
Visualizing the heat bounce helps us understand why the air stays warm even at night. The diagram illustrates how the CO₂ layer acts as a one-way gate for heat energy.
Teacher's Tip: Draw arrows that show light coming in straight and heat "bouncing" or "wiggling" back.
Exam Tip: If asked to draw this, clearly label "Incoming Solar Radiation" and "Outgoing Infrared Radiation."

Question 14:
Answer: 1. The warmer climate is changing the patterns of rainfall and snowfall. 2. It causes increase in the frequency and severity of drought and flood also. 3. It is affecting our resources like water, forests and different ecological systems. 4. It also cause frequent natural disasters like cyclones, storms and hurricanes, floods and droughts. 5. The global warming is damaging various ecosystems like mangrove-swamps, coral reefs and coastal lagoons, etc. due to various reasons like reduction in pH of oceanic water and increasing deposits of acids. 6. It is damaging the world biodiversity. Vast varieties of birds, reptiles, insects, bacteria, fungi, rodents etc. have vanished out due to these effects.
Melting polar ice caps cause sea levels to rise, which can flood coastal cities and destroy islands. Changes in temperature also mean that animals may lose their homes if they cannot migrate to cooler areas fast enough.
Teacher's Tip: Global warming makes the "Extremes" more extreme – hotter droughts and wetter floods.
Exam Tip: Mention "Biodiversity" to show how climate change impacts all living things, not just humans.

Question 15:
Answer: It has been found that in every southern spring(September-October) 50-95 % of stratospheric ozone is destroyed at a height of 15-24 kms above ‘Antarctica’ creating pockets which have been described as ozone hole.
The "hole" is actually a region where the ozone is extremely thin, allowing dangerous levels of UV light to pass through. This happens over Antarctica due to unique wind patterns and extremely cold temperatures that speed up destructive chemical reactions.
Teacher's Tip: Springtime in Antarctica is the most active time for the destruction of the ozone layer.
Exam Tip: Specify the exact percentage (50-95\%) and the location (Antarctica) to get maximum marks.

Question 16:
Answer: The adverse effects of ozone layer depletion are 1. UV radiation causes sun-eye diseases (cataract), skin diseases, skin cancer and damage to immune system in our body. 2. It damages plants and causes reduction in crop productivity. 3. It damages embryos of fish, shrimps, crabs and amphibians. 4. UV radiation damage fabrics, pipes, paints and other non-living materials on this earth. 5. It contributes in the global warming. If the ozone depletion continues, the temperature around the world may rise at faster rate and to a large extent.
UV radiation is powerful enough to penetrate human skin and damage our DNA, leading to mutations. In the oceans, UV light can kill the delicate larvae of sea creatures, which ruins the natural food chain.
Teacher's Tip: Think of Ozone depletion as "Earth getting a giant sunburn" that doesn't heal easily.
Exam Tip: List impacts on both living things (health/crops) and non-living materials (fabrics/paints) for a complete answer.

Question 17:
Answer: Natural greenhouse effect is a process of thermal blanketing of the earth which maintains its temperature to sustain life on it. Without greenhouse effect, the climate of the earth would be too cold for most of the life to survive.
The natural greenhouse effect is vital; without it, Earth would be a frozen ball of ice at around -18°C. It provides the perfect temperature range for liquid water and life to exist.
Teacher's Tip: Remember: The Greenhouse effect is a "friend" to life until pollution makes it too strong.
Exam Tip: Use the term "thermal blanketing" to describe how the earth stays warm naturally.

Question 18:
Answer: The effect of warming and insulation of the earth caused due to some heat trapping gases accumulated in the atmosphere after their emission from the earth surface is called as greenhouse effect. Due to this there is rise in the average global earth temperature called global warming.
Gases like CO₂ and methane allow energy from the sun to come in but block it from leaving. This creates a global warming trend that changes the environment for every living thing.
Teacher's Tip: Warming is the "result" while the Greenhouse Effect is the "process."
Exam Tip: Clearly link "heat trapping gases" to the rise in "average global temperature."

Question 19:
Answer: When an ozone molecule is hit by UV wavelengths, it absorbs the radiant energy and photo dissociates into O₂ and O giving off heat. Thus, keeps the UV radiation from reaching the earth’s surface and also causes a temperature inversion in the stratosphere that helps to maintain relatively stable climatic conditions on and near the ground.
Ozone acts like a protective shield that converts dangerous invisible light into harmless warmth. By doing this, it prevents the sun's most damaging rays from reaching us on the surface.
Teacher's Tip: Ozone doesn't just block UV; it "eats" the radiation and turns it into heat energy.
Exam Tip: Mention "temperature inversion" to show you understand how ozone stabilizes the stratosphere.

Question 20:
Answer: When an ozone molecule is hit by UV wavelengths, it absorbs the radiant energy and photo dissociates into O₂ and O giving off heat. Thus, keeps the UV radiation from reaching the earth’s surface and also causes a temperature inversion in the stratosphere that helps to maintain relatively stable climatic conditions on and near the ground.
This process is what makes the stratosphere unique compared to the layers above and below it. Without this absorption, life on land would be impossible due to high-energy radiation damage.
Teacher's Tip: Think of the stratosphere as Earth's "Ozone Sunscreen" layer.
Exam Tip: Use the term "photodissociates" to describe the breaking down of ozone molecules by light.