9th Class Chemistry Chapter # 10 Exercise Solutions – Punjab Board
Environmental Chemistry
1. Which gases are responsible for greenhouse effect?
(a) SO₂, NO₂
(b) NO, CO
(✓) (c) CO₂, CH₄
(d) O₃, N₂
Explanation:
Greenhouse gases like carbon dioxide (CO₂) and methane (CH₄) trap heat in the Earth’s atmosphere. This leads to the greenhouse effect, which causes global warming.
2. Indicate the source of sulphur oxides in the atmosphere.
(a) Decomposition/fertilization
(b) Waste gases from digestion of animals
(c) Photochemical smog
(✓) (d) Combustion of fossil fuels
Explanation:
When fossil fuels (coal, oil, diesel) are burned in industries or vehicles, they release sulphur dioxide (SO₂) into the air, which is a major air pollutant.
3. Which gas in the atmosphere is decreased by photosynthesis in plants?
(a) Oxygen
(b) Nitrogen
(✓) (c) Carbon dioxide
(d) Water vapours
Explanation:
During photosynthesis, green plants use carbon dioxide (CO₂) from the air and convert it into glucose and oxygen. So, CO₂ decreases in the atmosphere.
(iv) Which substance remains unaffected in the catalytic converter fixed in the exhaust of the automobiles?
(a) CO₂
(b) CO
(c) NO
(d) NO₂
✓ Correct Answer: (a) CO₂
Explanation:
Catalytic converters remove CO, NOₓ, and unburnt hydrocarbons. But CO₂ is not removed, as it is the end product of complete combustion.
(v) People of which age groups are most affected by the air pollution?
(a) Young adults
(b) Middle age people
(c) Children
✓ (d) Both children and aged people
Explanation:
Children have developing lungs and elderly have weak immune systems, so both are more vulnerable to polluted air and respiratory problems.
(vi) In which area there is a greater possibility of acid rain?
(a) Around village
(b) Around big cities
✓ (c) Around industrial area
(d) Around water bodies
Explanation:
Industrial areas emit large amounts of SO₂ and NOₓ, which combine with moisture in air to produce acid rain.
(vii) Why is smog not felt in summer?
✓ (a) Because fog is not present in summer
(b) Because due to heat of the Earth the smoke rises up
(c) Because in summer smoke and fog cannot mix with each other
(d) Because less fossil fuels are burnt in summer
Explanation:
Smog = smoke + fog. In summer, fog doesn’t form, so classical smog is not observed. However, photochemical smog can still occur.
(viii) Which catalyst is fixed in the exhaust sections of automobiles?
(a) Ni
(b) Cu
✓ (c) Pt, Pd and Rh
(d) CaO
Explanation:
Platinum (Pt), Palladium (Pd), and Rhodium (Rh) are used in catalytic converters to reduce harmful emissions in vehicle exhaust.
(ix) Which components are essential for the formation of photochemical smog?
(a) CO, NO₂, CO₂
✓ (b) NO₂, volatile organic compounds, sunlight
(c) CO₂, NO₂, sunlight
(d) Volatile organic compounds, NO₂, CO
Explanation:
Photochemical smog forms when sunlight reacts with NO₂ and VOCs (volatile organic compounds), producing ozone and other toxic chemicals.
(x) Which gases contribute towards the formation of acid rain?
(a) Oxides of carbon
(b) Oxides of sulphur
(c) Oxides of nitrogen
✓ (d) Both the oxides of nitrogen and sulfur
Explanation:
SO₂ and NOₓ gases react with water vapors in the air to form sulphuric and nitric acid, leading to acid rain.
Questions for Short Answers
1. What is the main objective of environmental education?
Answer:
The main objective of environmental education is to develop awareness, knowledge, and understanding about the environmental issues and to promote responsible behavior to protect and improve the natural environment.
It helps individuals become aware of problems like pollution, climate change, and conservation of resources.
2. How is particulate matter released in the atmosphere?
Answer:
Particulate matter (PM) is released into the atmosphere through:
Burning of fossil fuels (e.g., coal, diesel, petrol)
Construction and mining activities
Dust storms and volcanic eruptions
Industrial emissions and vehicle exhausts
These particles can be solid or liquid and remain suspended in air, causing air pollution and health problems.
3. Which gas is more poisonous, SO₂ or CO?
Answer:
Carbon monoxide (CO) is more poisonous than sulphur dioxide (SO₂).
CO binds with hemoglobin in the blood to form carboxyhemoglobin, which prevents oxygen from being transported to body tissues, causing suffocation and even death.
SO₂ is also harmful but mainly affects the respiratory system and causes irritation.
✅ Hence, CO is more dangerous due to its silent and fatal nature.
4. In what way sulphur present in fossil fuels becomes dangerous?
Answer:
Sulphur in fossil fuels like coal and oil burns to form sulphur dioxide (SO₂).
This SO₂ can:
React with water in the air to form sulphuric acid (H₂SO₄)
Lead to acid rain, which damages plants, aquatic life, buildings, and soil.
Cause breathing problems in humans.
✅ Thus, sulphur in fossil fuels contributes significantly to air pollution and acid rain.
5. Name any three major sources responsible for the greenhouse effect.
Answer:
Three major sources responsible for the greenhouse effect are:
Burning of fossil fuels – releases CO₂
Agricultural activities – release CH₄ (methane) from animals
Industrial emissions – emit nitrous oxide (N₂O) and other gases
These gases trap heat in the Earth’s atmosphere and cause global warming.
6. How is wind energy useful for us?
Answer:
Wind energy is a renewable source of energy used to:
Generate electricity through wind turbines
Reduce dependence on fossil fuels
Produce clean energy without causing pollution
Power remote or rural areas
✅ Wind energy is eco-friendly, sustainable, and helps combat climate change.