ROUTERA


Chapter 16 Environmental issues

Class 12th Biology Chapter MCQs


1. Which of the following is the major cause of air pollution?

  • A) Deforestation
  • B) Industrial emissions
  • C) Soil erosion
  • D) Water conservation

Answer: B
Explanation: Industrial emissions are one of the major causes of air pollution, as industries release large amounts of harmful gases like carbon dioxide (CO₂), sulfur dioxide (SO₂), and nitrogen oxides (NOₓ).


2. The ozone layer is important because it:

  • A) Protects us from harmful UV radiation
  • B) Contributes to global warming
  • C) Enhances the greenhouse effect
  • D) Controls acid rain

Answer: A
Explanation: The ozone layer absorbs and protects the Earth from harmful ultraviolet (UV) radiation from the sun, which can cause skin cancer, cataracts, and harm marine life.


3. Which of the following gases is mainly responsible for global warming?

  • A) Nitrogen
  • B) Oxygen
  • C) Carbon dioxide
  • D) Argon

Answer: C
Explanation: Carbon dioxide (CO₂) is a major greenhouse gas responsible for trapping heat in the Earth's atmosphere, leading to global warming.


4. What is the main cause of the depletion of the ozone layer?

  • A) Excessive use of fossil fuels
  • B) Use of chlorofluorocarbons (CFCs)
  • C) Deforestation
  • D) Increased nitrogen levels in the atmosphere

Answer: B
Explanation: Chlorofluorocarbons (CFCs), commonly used in air conditioners, refrigerators, and aerosol propellants, are the primary cause of the depletion of the ozone layer.


5. Which of the following is an effect of acid rain?

  • A) It enriches soil fertility
  • B) It leads to the neutralization of lakes
  • C) It damages aquatic life and soil
  • D) It reduces soil erosion

Answer: C
Explanation: Acid rain contains sulfuric and nitric acids that lower the pH of water bodies and soil, harming aquatic life and reducing soil fertility.


6. Which is the primary source of greenhouse gases?

  • A) Forest fires
  • B) Transportation and fossil fuel combustion
  • C) Volcanic eruptions
  • D) Solar radiation

Answer: B
Explanation: The major contributors to greenhouse gases are human activities such as fossil fuel combustion in transportation and industries, which release CO₂, methane (CH₄), and nitrous oxide (N₂O).


7. What is the main consequence of global warming?

  • A) Ocean cooling
  • B) Depletion of the ozone layer
  • C) Melting of polar ice caps
  • D) Increase in oxygen levels

Answer: C
Explanation: Global warming leads to the melting of polar ice caps, contributing to rising sea levels and altered weather patterns.


8. What is the primary cause of soil erosion?

  • A) Water scarcity
  • B) Forest fires
  • C) Deforestation and overgrazing
  • D) Industrialization

Answer: C
Explanation: Deforestation and overgrazing by livestock lead to the loss of topsoil, making the soil more prone to erosion by wind and water.


9. Which of the following is an example of a renewable resource?

  • A) Coal
  • B) Solar energy
  • C) Natural gas
  • D) Petroleum

Answer: B
Explanation: Solar energy is a renewable resource, as it is naturally replenished and does not deplete over time like fossil fuels.


10. Which of the following is not a greenhouse gas?

  • A) Methane (CH₄)
  • B) Nitrous oxide (N₂O)
  • C) Oxygen (O₂)
  • D) Carbon dioxide (CO₂)

Answer: C
Explanation: Oxygen (O₂) is not a greenhouse gas. Methane (CH₄), nitrous oxide (N₂O), and carbon dioxide (CO₂) are all greenhouse gases that trap heat in the atmosphere.


11. What is the most effective way to reduce the carbon footprint?

  • A) Increasing forest area
  • B) Reducing fossil fuel usage
  • C) Increasing water consumption
  • D) Burning more wood

Answer: B
Explanation: The most effective way to reduce the carbon footprint is by reducing fossil fuel usage, which directly lowers CO₂ emissions.


12. The term "biodiversity" refers to:

  • A) The variety of life forms present in an ecosystem
  • B) The total biomass of living organisms
  • C) The total number of species in the world
  • D) The abundance of a particular species in an area

Answer: A
Explanation: Biodiversity refers to the variety of life forms (species, ecosystems, and genetic diversity) present in an environment.


13. What is a major consequence of deforestation?

  • A) Decreased biodiversity
  • B) Increased oxygen production
  • C) Decreased carbon dioxide concentration
  • D) Increased water retention in soil

Answer: A
Explanation: Deforestation leads to decreased biodiversity, as habitats are destroyed, threatening plant and animal species.


14. What are the most significant sources of freshwater?

  • A) Oceans
  • B) Rivers and lakes
  • C) Atmosphere
  • D) Desalination plants

Answer: B
Explanation: Rivers and lakes are the primary sources of freshwater, which is essential for drinking, irrigation, and industrial use.


15. Which of the following methods can be used for water conservation?

  • A) Large-scale deforestation
  • B) Constructing dams and reservoirs
  • C) Reducing tree cover
  • D) Overuse of water resources

Answer: B
Explanation: Constructing dams and reservoirs helps in storing water, which can be used for irrigation and drinking during dry periods.


16. What is the major cause of the "greenhouse effect"?

  • A) Emission of greenhouse gases
  • B) Increased water vapor in the atmosphere
  • C) Excessive oxygen production
  • D) Increased UV radiation

Answer: A
Explanation: The greenhouse effect is caused by the emission of greenhouse gases, such as CO₂, CH₄, and N₂O, which trap heat in the Earth's atmosphere.


17. Which of the following is a consequence of acid rain?

  • A) Improvement in soil quality
  • B) Increase in the pH of lakes
  • C) Decreased soil fertility and damage to aquatic life
  • D) Increased oxygen levels in water bodies

Answer: C
Explanation: Acid rain lowers the pH of lakes and soils, which harms aquatic life and reduces soil fertility.


18. Which one of the following is a sustainable practice for reducing environmental damage?

  • A) Over-exploitation of natural resources
  • B) Use of renewable energy sources
  • C) Overfishing
  • D) Deforestation for urban expansion

Answer: B
Explanation: The use of renewable energy sources, such as solar, wind, and hydroelectric power, is a sustainable practice that helps reduce environmental damage.


19. Which of the following causes the depletion of the ozone layer?

  • A) Greenhouse gases
  • B) Nitrous oxide emissions
  • C) Chlorofluorocarbons (CFCs)
  • D) Sulfur dioxide emissions

Answer: C
Explanation: Chlorofluorocarbons (CFCs) are the primary cause of the depletion of the ozone layer, as they break down ozone molecules in the stratosphere.


20. Which of the following is a common method for waste disposal?

  • A) Recycling
  • B) Deforestation
  • C) Increased water usage
  • D) Agricultural burning

Answer: A
Explanation: Recycling is an effective method for waste disposal as it helps reduce landfill waste and recycles materials for reuse.


21. Which of the following is responsible for the greenhouse effect?

  • A) Chlorofluorocarbons (CFCs)
  • B) Greenhouse gases like CO₂
  • C) Ozone depletion
  • D) Sulfur dioxide (SO₂)

Answer: B
Explanation: The greenhouse effect is caused by the accumulation of greenhouse gases such as carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O), which trap heat in the atmosphere.


22. The ozone layer is mainly located in which part of the atmosphere?

  • A) Troposphere
  • B) Stratosphere
  • C) Mesosphere
  • D) Exosphere

Answer: B
Explanation: The ozone layer is located in the stratosphere, where it absorbs most of the sun's harmful ultraviolet (UV) radiation.


23. Which of the following is a renewable resource?

  • A) Coal
  • B) Petroleum
  • C) Solar energy
  • D) Natural gas

Answer: C
Explanation: Solar energy is a renewable resource, as it is naturally replenished and does not deplete over time.


24. What is the main cause of global warming?

  • A) Excessive rainfall
  • B) Increasing levels of greenhouse gases
  • C) Solar flares
  • D) Deforestation

Answer: B
Explanation: The main cause of global warming is the increasing concentration of greenhouse gases in the atmosphere, which trap heat.


25. Which one of the following gases contributes most to the greenhouse effect?

  • A) Nitrogen
  • B) Oxygen
  • C) Methane
  • D) Carbon dioxide

Answer: D
Explanation: Carbon dioxide (CO₂) is the most significant greenhouse gas contributing to the greenhouse effect and global warming.


26. Which of the following is an example of a non-renewable resource?

  • A) Wind energy
  • B) Solar energy
  • C) Coal
  • D) Geothermal energy

Answer: C
Explanation: Coal is a non-renewable resource, as it takes millions of years to form and cannot be replenished on a human timescale.


27. What is the result of the accumulation of CO₂ in the atmosphere?

  • A) Global cooling
  • B) Global warming
  • C) Increase in rainfall
  • D) Ozone depletion

Answer: B
Explanation: The accumulation of carbon dioxide (CO₂) and other greenhouse gases leads to global warming, which results in rising temperatures.


28. Which of the following contributes to the depletion of the ozone layer?

  • A) Carbon dioxide
  • B) Methane
  • C) Nitrous oxide
  • D) Chlorofluorocarbons (CFCs)

Answer: D
Explanation: Chlorofluorocarbons (CFCs) are the primary substances responsible for the depletion of the ozone layer, as they break down ozone molecules in the stratosphere.


29. Which of the following is a consequence of global warming?

  • A) Increased biodiversity
  • B) Melting of polar ice caps
  • C) Reduction in sea levels
  • D) Increased oxygen levels in the atmosphere

Answer: B
Explanation: Global warming leads to the melting of polar ice caps, contributing to rising sea levels and more extreme weather events.


30. The primary source of energy for life on Earth is:

  • A) Geothermal energy
  • B) Solar energy
  • C) Wind energy
  • D) Nuclear energy

Answer: B
Explanation: Solar energy is the primary source of energy for life on Earth. It drives photosynthesis in plants and is the basis for most food chains.


31. Which of the following is the most effective method to control soil erosion?

  • A) Overgrazing
  • B) Deforestation
  • C) Afforestation
  • D) Mining

Answer: C
Explanation: Afforestation (planting trees) helps control soil erosion by stabilizing the soil with plant roots, preventing soil loss due to wind and water.


32. What does the term 'biodiversity' refer to?

  • A) The total number of species in a region
  • B) The variety of ecosystems
  • C) The variety of life forms, including species, ecosystems, and genetic diversity
  • D) The abundance of a particular species

Answer: C
Explanation: Biodiversity refers to the variety of life forms, including species diversity, ecosystem diversity, and genetic diversity.


33. What is the role of microorganisms in environmental conservation?

  • A) They contribute to global warming
  • B) They degrade pollutants and recycle nutrients
  • C) They are harmful to plants and animals
  • D) They produce greenhouse gases

Answer: B
Explanation: Microorganisms play a crucial role in degrading pollutants and recycling nutrients, thus contributing to environmental conservation.


34. Which of the following is an example of non-biodegradable waste?

  • A) Paper
  • B) Plastic
  • C) Vegetable matter
  • D) Food scraps

Answer: B
Explanation: Plastic is an example of non-biodegradable waste, as it does not decompose naturally and accumulates in the environment.


35. Which of the following can help in controlling air pollution?

  • A) Burning of fossil fuels
  • B) Planting more trees
  • C) Increased industrial activities
  • D) Use of chlorofluorocarbons (CFCs)

Answer: B
Explanation: Planting trees helps in absorbing carbon dioxide and releasing oxygen, which can help reduce air pollution.


36. Which of the following gases is released by vehicles and contributes to air pollution?

  • A) Oxygen
  • B) Nitrogen
  • C) Carbon monoxide
  • D) Methane

Answer: C
Explanation: Carbon monoxide (CO) is released by vehicles during the combustion of fossil fuels, and it is a major contributor to air pollution.


37. What is the main component of smog?

  • A) Ozone
  • B) Nitrogen
  • C) Sulfur dioxide
  • D) Carbon dioxide

Answer: A
Explanation: Smog is a mixture of ozone (O₃), particulate matter, and other air pollutants, which are harmful to human health.


38. Which of the following is a potential solution for reducing environmental pollution?

  • A) Reducing the use of pesticides
  • B) Burning fossil fuels
  • C) Expanding urbanization
  • D) Increasing the use of CFCs

Answer: A
Explanation: Reducing the use of pesticides helps minimize their impact on soil and water pollution, thus benefiting the environment.


39. The effect of acid rain on aquatic life is primarily due to:

  • A) Decreased oxygen levels
  • B) Increased water temperature
  • C) Reduced light penetration
  • D) Decreased pH levels in water

Answer: D
Explanation: Acid rain lowers the pH levels of water bodies, which harms aquatic life by disrupting their natural biological processes.


40. Which of the following is true about sustainable development?

  • A) It focuses only on economic growth
  • B) It involves exploitation of natural resources without any limitations
  • C) It balances economic growth, environmental protection, and social equity
  • D) It neglects the conservation of biodiversity

Answer: C
Explanation: Sustainable development seeks to balance economic growth, environmental protection, and social equity to ensure long-term prosperity.


41. Which of the following gases is responsible for ozone layer depletion?

  • A) Methane
  • B) Carbon dioxide
  • C) Chlorofluorocarbons (CFCs)
  • D) Oxygen

Answer: C
Explanation: Chlorofluorocarbons (CFCs) are primarily responsible for the depletion of the ozone layer, as they break down ozone molecules in the stratosphere.


42. Which of the following is the most significant contributor to the greenhouse effect?

  • A) Nitrous oxide
  • B) Carbon dioxide
  • C) Methane
  • D) Water vapor

Answer: B
Explanation: Carbon dioxide (CO₂) is the most significant contributor to the greenhouse effect and global warming.


43. What is the process by which energy is transferred in an ecosystem?

  • A) Photosynthesis
  • B) Respiration
  • C) Food chain
  • D) Transpiration

Answer: C
Explanation: In an ecosystem, energy transfer occurs through the food chain, where energy is passed from producers to consumers and decomposers.


44. Which of the following is a major environmental issue associated with the use of fertilizers?

  • A) Water contamination and eutrophication
  • B) Increased biodiversity
  • C) Soil fertility improvement
  • D) Carbon emission

Answer: A
Explanation: The use of fertilizers can lead to water contamination and eutrophication, which degrades water quality and harms aquatic ecosystems.


45. Which of the following is an example of a renewable source of energy?

  • A) Coal
  • B) Petroleum
  • C) Solar energy
  • D) Natural gas

Answer: C
Explanation: Solar energy is a renewable energy source, as it is naturally replenished and does not deplete over time.


46. Which of the following is a direct consequence of deforestation?

  • A) Increased soil fertility
  • B) Decreased biodiversity
  • C) Reduced carbon dioxide in the atmosphere
  • D) Increased rainfall

Answer: B
Explanation: Deforestation leads to the loss of biodiversity as it destroys habitats for many species.


47. Which of the following is a method used to reduce the impact of soil erosion?

  • A) Overgrazing
  • B) Afforestation
  • C) Excessive mining
  • D) Construction of dams

Answer: B
Explanation: Afforestation helps reduce soil erosion by providing vegetative cover that stabilizes the soil with roots.


48. What is the primary cause of the depletion of the ozone layer?

  • A) Carbon dioxide
  • B) Sulfur dioxide
  • C) Chlorofluorocarbons (CFCs)
  • D) Methane

Answer: C
Explanation: Chlorofluorocarbons (CFCs) are the primary cause of ozone layer depletion, as they break down ozone molecules in the stratosphere.


49. Which of the following is a benefit of using biofuels?

  • A) Reduced carbon footprint
  • B) Increased air pollution
  • C) Decreased water availability
  • D) Decreased agricultural productivity

Answer: A
Explanation: Biofuels contribute to a reduced carbon footprint because they are renewable and produce fewer emissions compared to fossil fuels.


50. Which of the following is a measure to prevent air pollution?

  • A) Use of catalytic converters in vehicles
  • B) Deforestation
  • C) Increase in industrial emissions
  • D) Burning of fossil fuels

Answer: A
Explanation: The use of catalytic converters in vehicles helps reduce the emission of harmful gases like carbon monoxide, nitrogen oxides, and hydrocarbons, thus preventing air pollution.