MCQs on Environmental Issues – CBSE Biology Class 12

MCQs on Environmental Issues – CBSE Biology Class 12 (NCERT Based)

Course: CBSE Class 12 Biology
Unit V: Ecology and Environment
Topic: Environmental Issues

The following 50 Multiple Choice Questions (MCQs) are strictly based on the NCERT syllabus and framed as per CBSE board examination standards. The questions are arranged section-wise, and each MCQ is followed by the correct answer with a detailed, concept-clearing explanation, making them ideal for board exam preparation and revision.

Section A: Air Pollution and Its Control (Q1–Q15)

Q1. Which of the following is a primary air pollutant?
A. Ozone
B. Sulphur dioxide
C. PAN
D. Acid rain

Answer: B
Explanation: Primary pollutants like sulphur dioxide are released directly from sources such as burning fossil fuels.

Q2. Smog formed in metropolitan cities is mainly due to:
A. SO₂ and CO
B. NO₂ and hydrocarbons
C. CO₂ and methane
D. Chlorofluorocarbons

Answer: B
Explanation: Photochemical smog forms due to nitrogen oxides and hydrocarbons under sunlight.

Q3. Which gas is mainly responsible for global warming?
A. Nitrogen
B. Oxygen
C. Carbon dioxide
D. Hydrogen

Answer: C
Explanation: Carbon dioxide traps heat in the atmosphere, contributing to the greenhouse effect.

Q4. Which of the following causes acid rain?
A. CO₂ and CH₄
B. SO₂ and NO₂
C. O₃ and CO
D. CFCs

Answer: B
Explanation: Sulphur dioxide and nitrogen dioxide react with water vapour to form acidic compounds.

Q5. Which pollutant reduces oxygen-carrying capacity of blood?
A. Carbon dioxide
B. Sulphur dioxide
C. Carbon monoxide
D. Ozone

Answer: C
Explanation: Carbon monoxide binds strongly with haemoglobin to form carboxyhaemoglobin.

Q6. Particulate matter smaller than 2.5 microns is called:
A. PM10
B. PM5
C. PM2.5
D. SPM

Answer: C
Explanation: PM2.5 particles are extremely harmful as they penetrate deep into lungs.

Q7. Which disease is commonly caused by air pollution?
A. Typhoid
B. Asthma
C. Malaria
D. Dengue

Answer: B
Explanation: Air pollutants irritate respiratory passages, leading to asthma and bronchitis.

Q8. Which gas causes chlorosis in plants?
A. CO₂
B. SO₂
C. Nitrogen
D. Methane

Answer: B
Explanation: Sulphur dioxide damages chlorophyll, causing yellowing of leaves.

Q9. Vehicular emissions can be reduced by using:
A. Diesel engines
B. Leaded petrol
C. Catalytic converters
D. Coal

Answer: C
Explanation: Catalytic converters convert toxic gases into less harmful substances.

Q10. The Air (Prevention and Control of Pollution) Act in India was enacted in:
A. 1972
B. 1981
C. 1986
D. 1991

Answer: B
Explanation: The Act aims to control and prevent air pollution.

Q11. Which is a secondary air pollutant?
A. CO
B. SO₂
C. PAN
D. Lead

Answer: C
Explanation: PAN (Peroxyacetyl nitrate) forms secondarily in the atmosphere.

Q12. Which gas is released during incomplete combustion of fuels?
A. CO₂
B. CO
C. SO₂
D. NO₂

Answer: B
Explanation: Incomplete combustion releases carbon monoxide.

Q13. Indoor air pollution is mainly caused by:
A. LPG
B. Biomass fuel
C. Electricity
D. Solar energy

Answer: B
Explanation: Burning biomass produces smoke and harmful gases indoors.

Q14. Which pollutant causes irritation of eyes and throat?
A. Ozone
B. Nitrogen
C. Hydrogen
D. Helium

Answer: A
Explanation: Ozone is a strong oxidant causing eye and respiratory irritation.

Q15. Smog reduces visibility because it contains:
A. Dust and smoke
B. Water vapour
C. CO₂
D. Nitrogen

Answer: A
Explanation: Smog is a mixture of smoke and fog, reducing visibility.

Section B: Water Pollution and Its Control (Q16–Q30)

Q16. Which parameter indicates organic pollution in water?
A. pH
B. BOD
C. COD
D. Turbidity

Answer: B
Explanation: Biological Oxygen Demand measures organic matter in water.

Q17. Eutrophication is caused by excessive:
A. Pesticides
B. Heavy metals
C. Nutrients
D. Salts

Answer: C
Explanation: Excess nitrates and phosphates promote algal blooms.

Q18. Which organism is used as an indicator of water pollution?
A. Frog
B. Fish
C. Algae
D. Bacteria

Answer: C
Explanation: Algal blooms indicate nutrient enrichment of water bodies.

Q19. Water hyacinth is called the “terror of Bengal” because it:
A. Is poisonous
B. Consumes oxygen rapidly
C. Blocks waterways
D. Releases toxins

Answer: C
Explanation: It grows rapidly and chokes aquatic ecosystems.

Q20. Which treatment removes organic matter from sewage?
A. Primary treatment
B. Secondary treatment
C. Tertiary treatment
D. Chemical treatment

Answer: B
Explanation: Secondary treatment uses microorganisms to degrade organic matter.

Q21. Minamata disease is caused by:
A. Lead
B. Mercury
C. Arsenic
D. Cadmium

Answer: B
Explanation: It is caused by methyl mercury poisoning.

Q22. Excess fluoride in drinking water causes:
A. Goitre
B. Anaemia
C. Fluorosis
D. Rickets

Answer: C
Explanation: Fluoride accumulation leads to bone and dental deformities.

Q23. Thermal pollution mainly affects:
A. Soil
B. Air
C. Aquatic organisms
D. Humans

Answer: C
Explanation: Increased water temperature reduces dissolved oxygen, harming aquatic life.

Q24. Which industry releases organic effluents?
A. Thermal power plants
B. Sugar mills
C. Cement industry
D. Steel industry

Answer: B
Explanation: Sugar mills discharge organic wastes increasing BOD.

Q25. Which process removes heavy metals from wastewater?
A. Sedimentation
B. Filtration
C. Ion exchange
D. Chlorination

Answer: C
Explanation: Ion exchange removes toxic metal ions.

Q26. Sewage rich in nutrients leads to:
A. Biomagnification
B. Eutrophication
C. Acid rain
D. Greenhouse effect

Answer: B
Explanation: Nutrient enrichment causes excessive plant growth.

Q27. Which gas is released from anaerobic sewage treatment?
A. Oxygen
B. Methane
C. Nitrogen
D. Carbon monoxide

Answer: B
Explanation: Anaerobic bacteria produce biogas rich in methane.

Q28. Which pollutant causes biomagnification?
A. Nitrates
B. DDT
C. CO₂
D. Sulphates

Answer: B
Explanation: Persistent pesticides like DDT accumulate along food chains.

Q29. Water pollution mainly affects:
A. Only humans
B. Only plants
C. Aquatic ecosystems
D. Terrestrial ecosystems

Answer: C
Explanation: Aquatic organisms are directly exposed to water pollutants.

Q30. Primary treatment of sewage involves:
A. Microbial action
B. Chemical oxidation
C. Physical removal of solids
D. UV treatment

Answer: C
Explanation: It removes floating and suspended solids.

Section C: Solid Waste, Noise Pollution & Other Issues (Q31–Q50)

Q31. Solid waste management follows which principle?
A. Reduce, Reuse, Recycle
B. Use, Dump, Forget
C. Burn, Bury, Ignore
D. Collect and Dump

Answer: A
Explanation: The 3R principle minimizes waste generation.

Q32. Which waste is biodegradable?
A. Plastic
B. Glass
C. Vegetable waste
D. Metal

Answer: C
Explanation: Organic waste decomposes naturally by microorganisms.

Q33. Noise pollution is measured in:
A. Hertz
B. Decibel
C. Watt
D. Ampere

Answer: B
Explanation: Noise intensity is measured in decibels (dB).

Q34. Prolonged exposure to noise can cause:
A. Blindness
B. Deafness
C. Skin disease
D. Anaemia

Answer: B
Explanation: Continuous loud noise damages auditory nerves.

Q35. Which is a non-biodegradable waste?
A. Paper
B. Cotton
C. Plastic
D. Wood

Answer: C
Explanation: Plastic persists in the environment for long periods.

Q36. E-waste contains toxic metals like:
A. Iron
B. Aluminium
C. Mercury
D. Sodium

Answer: C
Explanation: Mercury in e-waste is highly toxic.

Q37. Ozone layer depletion is caused by:
A. CO₂
B. SO₂
C. CFCs
D. NO₂

Answer: C
Explanation: CFCs release chlorine that destroys ozone molecules.

Q38. Which radiation increases due to ozone depletion?
A. Infrared
B. Gamma
C. UV-B
D. X-ray

Answer: C
Explanation: UV-B causes skin cancer and DNA damage.

Q39. Greenhouse effect leads to:
A. Global cooling
B. Acid rain
C. Global warming
D. Ozone formation

Answer: C
Explanation: Trapping of heat raises Earth’s average temperature.

Q40. Which gas has the highest global warming potential?
A. CO₂
B. CH₄
C. N₂O
D. CFCs

Answer: D
Explanation: CFCs trap maximum heat per molecule.

Q41. Which international agreement controls CFCs?
A. Kyoto Protocol
B. Montreal Protocol
C. Paris Agreement
D. Ramsar Convention

Answer: B
Explanation: The Montreal Protocol aims to protect the ozone layer.

Q42. Which practice helps in waste reduction?
A. Landfilling
B. Incineration
C. Recycling
D. Dumping

Answer: C
Explanation: Recycling reduces resource use and pollution.

Q43. Noise above safe limits affects:
A. Nervous system
B. Digestive system
C. Circulatory system
D. Excretory system

Answer: A
Explanation: Noise causes stress and mental disturbances.

Q44. Which of the following is a renewable energy source?
A. Coal
B. Petroleum
C. Wind
D. Natural gas

Answer: C
Explanation: Wind energy is sustainable and non-polluting.

Q45. Landfills mainly create which problem?
A. Water scarcity
B. Groundwater pollution
C. Noise pollution
D. Ozone depletion

Answer: B
Explanation: Leachates from landfills contaminate groundwater.

Q46. Which pollutant causes blue baby syndrome?
A. Phosphates
B. Nitrates
C. Sulphates
D. Chlorides

Answer: B
Explanation: High nitrates reduce oxygen supply in infants.

Q47. Which method converts waste into energy?
A. Composting
B. Recycling
C. Incineration
D. Landfilling

Answer: C
Explanation: Incineration produces energy from waste burning.

Q48. Which is an eco-friendly alternative to plastic bags?
A. Polythene
B. Paper bags
C. PVC bags
D. Nylon bags

Answer: B
Explanation: Paper bags are biodegradable.

Q49. The Environment Protection Act in India was enacted in:
A. 1972
B. 1981
C. 1986
D. 1991

Answer: C
Explanation: The Act provides comprehensive environmental protection.

Q50. Environmental issues can be best controlled by:
A. Laws alone
B. Technology alone
C. Public awareness and participation
D. Industrial growth

Answer: C
Explanation: Sustainable solutions require active public involvement and awareness.

✅ NCERT-Aligned | CBSE Board Exam Ready | Concept-Focused MCQs