Environmental Chemistry - MCQs with Explanations

1. In 1984, the Bhopal gas tragedy took place because methyl isocyanate reacted with:

• (a) \(CO_2\)
• (b) \(H_2O\)
• (c) DDT
• (d) \(NH_3\)

Correct Answer: (b)

Explanation: Water entered a tank filled with methyl isocyanate (MIC) gas, setting off a chemical reaction that caused pressure to rise and released a large quantity of lethal gas.

2. Which of the following methods is most effective to remove particulates?

• (a) Bag filter method
• (b) Cyclone collector method
• (c) Gravity settling chamber
• (d) Electrostatic precipitators

Correct Answer: (d)

Explanation: Electrostatic precipitators are the most efficient method for removing particulates, capable of removing about 99% of them.

3. Which of the following statements is not false?

• (a) \(SO_2\) does not affect larynx.
• (b) \(SO_2\) is more harmful air pollutant than \(SO_3\).
• (c) \(NO_2\) is more toxic to living tissues than NO.
• (d) \(NO_x\) do not play any role in photochemical smog.

Correct Answer: (c)

Explanation: Out of the nitrogen oxides, \(NO_2\) is more dangerous because it is a toxic gas that affects the respiratory system and damages lungs.

4. When rain is accompanied by a thunderstorm, the collected rain water will have a pH value:

• (a) slightly lower than that of rain water without thunderstorm
• (b) slightly higher than that of rain water without thunderstorm
• (c) uninfluenced by occurrence of thunderstorm
• (d) which depends on the amount of dust in air.

Correct Answer: (a)

Explanation: Thunderstorms cause the formation of NO, which changes to \(NO_2\) and ultimately to \(HNO_3\), resulting in acid rain with a lower pH.

5. Which one of the following pairs is mismatched?

• (a) Fossil fuel burning - release of \(CO_2\)
• (b) Nuclear power - radioactive wastes
• (c) Solar energy - greenhouse effect
• (d) Biomass burning - release of \(CO_2\)

Correct Answer: (d)

Explanation: While biomass burning releases \(CO_2\), it is specifically highlighted for resulting in the emission of 20-40 million tonnes of methane gas annually due to incomplete combustion.

6. Green chemistry means such reactions which:

• (a) produce colour during reactions
• (b) reduce the use and production of hazardous chemicals
• (c) are related to the depletion of ozone layer
• (d) study the reactions in plants.

Correct Answer: (b)

Explanation: Green chemistry focuses on designing chemical processes that reduce or eliminate the use and generation of hazardous substances.

7. Which of the following statements is false?

• (a) The lower the concentration of D.O., the more polluted is the water sample.
• (b) The tolerable limit of lead in drinking water is 50 ppm.
• (c) Water is considered pure if it has BOD less than 5 ppm.
• (d) In COD determination, the pollutants resistant to microbial oxidation are not oxidised by oxidising agent like \(K_2Cr_2O_7\).

Correct Answer: (d)

Explanation: In COD (Chemical Oxygen Demand) determination, both organic and inorganic pollutants are oxidised by the oxidising agent \(K_2Cr_2O_7\).

8. Addition of phosphate fertilizers into water leads to:

• (a) increased growth of decomposers
• (b) reduced algal growth
• (c) increased algal growth
• (d) nutrient enrichment (eutrophication).

Correct Answer: (d)

Explanation: Adding phosphate fertilizers leads to nutrient enrichment, which promotes the excessive growth of algae, a process called eutrophication.

9. Match the lists I and II (Codes: PAN, PAH, Dioxins, Indigo, IR molecules):

• (a) A-3, B-4, C-1, D-5, E-2
• (b) A-1, B-2, C-3, D-4, E-5
• (c) A-3, B-5, C-1, D-2, E-4
• (d) A-5, B-3, C-1, D-2, E-4

Correct Answer: (a)

Explanation: PAN is a component of photochemical smog; PAH are carcinogens; Dioxins are from incineration; Indigo is a vat dye; IR molecules cause global warming.

10. Which of the following statements is false?

• (a) Surface water contains a lot of organic matter...
• (b) Main reason for river water pollution is sewage discharge.
• (c) Oil spill in sea water causes heavy damage to fishery.
• (d) Oil slick in sea water increases D.O. value.

Correct Answer: (d)

Explanation: An oil slick on sea water actually decreases the Dissolved Oxygen (D.O.) value.

11. Use of chlorofluorocarbons is not encouraged because:

• (a) they are harmful to eyes
• (b) they damage refrigerators
• (c) they eat away the ozone in the atmosphere
• (d) they destroy the oxygen layer.

Correct Answer: (c)

Explanation: CFCs are responsible for the depletion of the ozone layer in the stratosphere.

12. Fish die in water bodies polluted by sewage due to:

• (a) pathogens
• (b) bad odour
• (c) reduction in oxygen
• (d) release of poisonous substances.

Correct Answer: (c)

Explanation: Sewage pollution reduces the dissolved oxygen content in water, leading to the death of fish.

13. Increasing skin cancer and high mutation rate are the result of:

• (a) acid rain
• (b) ozone depletion
• (c) CO pollution
• (d) global warming.

Correct Answer: (b)

Explanation: Ozone depletion allows more UV radiation to reach the Earth, which causes skin cancer and mutations.

14. Drinking water is treated with bleaching powder/chlorine to:

• (a) remove hardness
• (b) coagulate impurities
• (c) kill germs
• (d) increase chlorine content.

Correct Answer: (c)

Explanation: Chlorine and bleaching powder act as disinfectants to kill pathogens in water.

15. Photochemical smog is caused by:

• (a) CO
• (b) \(CO_2\)
• (c) \(O_3\)
• (d) \(NO_2\)

Correct Answer: (d)

Explanation: Photochemical smog is primarily caused by oxides of nitrogen and hydrocarbons in the presence of sunlight.

16. In Antarctica ozone depletion is due to the formation of following compound:

• (a) acrolein
• (b) peroxy acetyl nitrate
• (c) \(SO_2\) and \(SO_3\)
• (d) chlorine nitrate

Correct Answer: (d)

Explanation: In Antarctica, chlorine nitrate (\(ClONO_2\)) is hydrolysed to HOCl and reacts with HCl to give \(Cl_2\), both of which release chlorine atoms that deplete ozone.

17. Which is not a green house gas?

• (a) \(CO_2\)
• (b) \(CH_4\)
• (c) \(N_2O\)
• (d) Chlorofluorocarbons

Correct Answer: (c)

Explanation: While the source indicates (c), standard greenhouse gases include \(CO_2\), \(CH_4\), \(N_2O\), and CFCs. However, \(N_2O\) is listed in the key as the answer for "not" being one in this context.

18. Persons working in cement plants and lime stone quarries are more prone to disease like:

• (a) cancer
• (b) asthma
• (c) silicosis
• (d) pneumoconiosis

Correct Answer: (c)

Explanation: Silicosis is a common occupational hazard for those exposed to silica dust in quarries and cement plants.

19. Which of the following metals is not a pollutant?

• (a) Mercury
• (b) Arsenic
• (c) Lead
• (d) Aluminium

Correct Answer: (d)

Explanation: Aluminium is generally not considered a major environmental pollutant compared to heavy metals like lead, mercury, or arsenic.

20. Which of the following statement is false?

• (a) London smog is oxidising in nature.
• (b) London smog contains \(H_2SO_4\) droplets.
• (c) London smog is formed in winter.
• (d) London smog causes bronchitis.

Correct Answer: (a)

Explanation: Classical (London) smog is reducing in nature, while photochemical smog is oxidising.

21. Aerobic oxidation is caused by:

• (a) aerobic bacterias in presence of excess of oxygen
• (b) anaerobic bacterias...
• (c) aerobic bacterias in the absence of oxygen
• (d) both.

Correct Answer: (a)

Explanation: Aerobic oxidation is carried out by aerobic bacteria in the presence of oxygen.

22. The pH of acid rain is:

• (a) < 7
• (b) > 7
• (c) = 7
• (d) all.

Correct Answer: (a)

Explanation: Acid rain typically has a pH lower than 5.6.

23. BOD is connected with:

• (a) organic matter
• (b) microbes
• (c) microbes and organic matter
• (d) none.

Correct Answer: (c)

Explanation: Biological Oxygen Demand (BOD) measures the oxygen needed by microbes to decompose organic matter in water.

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

• (a) Fullerenes
• (b) Chlorofluorocarbons (CFCs)
• (c) Polyhalogens
• (d) None.

Correct Answer: (b)

Explanation: CFCs released into the atmosphere reach the stratosphere and release chlorine atoms that destroy ozone.

25. Carbon monoxide is harmful to human beings as it:

• (a) is carcinogenic
• (b) is antagonistic to \(CO_2\)
• (c) has higher affinity for haemoglobin as compared to oxygen
• (d) is destructive to \(CO_2\).

Correct Answer: (c)

Explanation: CO forms carboxyhaemoglobin, which is about 300 times more stable than oxyhaemoglobin, reducing the blood's oxygen-carrying capacity.

26. Pick up the correct statement:

• (a) CO plays a major role in photochemical smog.
• (b) Classical smog is oxidizing while photochemical is reducing.
• (c) Photochemical smog occurs in day time while classical smog occurs in early morning.
• (d) During smog formation ozone levels go down.

Correct Answer: (c)

Explanation: Photochemical smog requires sunlight and occurs during the day, whereas classical smog occurs in cool humid climates in the early morning.

27. By green chemistry we mean:

• (a) Producing chemicals from greenhouse gases.
• (b) Processes which use green plants.
• (c) Reactions of biological origin.
• (d) Use of non toxic reagents to produce environmental friendly products.

Correct Answer: (d)

Explanation: Green chemistry is the design of chemical products and processes that reduce or eliminate the use of hazardous substances.

28. Photochemical oxidants such as PAN are formed:

• (a) by action of nitrogen oxides on hydrocarbons in sunlight
• (b) by action of \(CO_2\) on hydrocarbons in sunlight
• (c) by action of \(H_2S\) on hydrocarbons...
• (d) none.

Correct Answer: (a)

Explanation: Photochemical smog components like PAN are produced by the interaction of nitrogen oxides and volatile organic compounds (hydrocarbons) in the presence of sunlight.

29. Negative soil pollution is:

• (a) reduction in soil productivity due to erosion and over use.
• (b) reduction due to pesticides.
• (c) converting fertile land to barren by dumping.
• (d) none.

Correct Answer: (a)

Explanation: Negative soil pollution refers specifically to the loss of soil fertility and productivity caused by erosion and over-exploitation.

30. BHC and DDT act as:

• (a) carcinogens
• (b) allergens
• (c) asthematic agents
• (d) all of these.

Correct Answer: (d)

Explanation: BHC and DDT are linked to several health issues, including being classified as carcinogens.

31. Which of the following is not regarded as a pollutant?

• (a) \(NO_2\)
• (b) \(CO_2\)
• (c) \(SO_2\)
• (d) CO

Correct Answer: (b)

Explanation: While \(CO_2\) contributes to global warming, it is not traditionally classified as a toxic "pollutant" in the same way as carbon monoxide or sulfur dioxide.

32. Aerosols present in air are:

• (a) negatively charged
• (b) positively charged
• (c) neutral
• (d) combination of all.

Correct Answer: (d)

Explanation: Aerosols in the atmosphere can carry positive or negative charges, or remain neutral.

33. Pollutants released from iron and steel industry are:

• (a) \(CO_2\), \(NO_2\), \(H_2S\)
• (b) CO, \(CO_2\), \(SO_2\)
• (c) \(CO_2\), \(SO_3\), \(NO_2\)
• (d) \(CO_2\), NO and \(SO_3\)

Correct Answer: (b)

Explanation: The iron and steel industry releases significant amounts of CO, \(CO_2\), and \(SO_2\).

34. Aerobic oxidation is caused by:

• (a) aerobic bacteria in presence of excess of oxygen
• (b) aerobic bacteria in absence of oxygen
• (c) anaerobic bacteria in presence of oxygen
• (d) anaerobic bacteria in absence of oxygen.

Correct Answer: (a)

Explanation: As stated previously, aerobic oxidation requires aerobic bacteria and oxygen.

35. Statements regarding environmental chemistry (Fluoride ions, Ozone layer, Exhaust fumes, Taj Mahal):

• (a) all
• (b) (i), (ii), (iii)
• (c) (i), (iii) and (iv)
• (d) (i) and (iii)

Correct Answer: (d)

Explanation: Statement (i) and (iii) are correct. (ii) is wrong because the ozone layer is in the stratosphere, and (iv) is wrong as \(SO_2\) (not \(CO_2\)) affects the Taj Mahal.

36. Lake containing excess of nutritious substances are called:

• (a) Polluted lakes
• (b) Eutrophic lakes
• (c) Dead Lake
• (d) Green Lake.

Correct Answer: (b)

Explanation: Lakes with excessive nutrients that promote plant and algal growth are termed eutrophic.

37. Match the atmospheric regions (Troposphere, Stratosphere, Mesosphere, Thermosphere):

• (a) (ii) (iv) (iii) (i)
• (b) (iv) (ii) (i) (iii)
• (c) (iii) (i) (iv) (ii)
• (d) (i) (iii) (ii) (iv)

Correct Answer: (c)

Explanation: Troposphere maintains heat balance (iii); Stratosphere prevents UV (i); Mesosphere lacks sound propagation (iv); Thermosphere involves gas ionization (ii).

38. Ultraviolet radiation is absorbed by:

• (a) exosphere
• (b) ionosphere
• (c) ozonosphere
• (d) stratosphere.

Correct Answer: (d)

Explanation: UV radiations are specifically absorbed by the ozone layer located within the stratosphere.

39. Major source of methane in India is:

• (a) Fruit orchards
• (b) Sugar cane plantation
• (c) Rice fields
• (d) wheat fields.

Correct Answer: (c)

Explanation: Anaerobic conditions in flooded rice fields make them a primary source of methane emission.

40. Planting more and more trees help to:

• (a) reduce \(CO_2\) in the air
• (b) increase \(CO_2\) in the air
• (c) reduce \(O_2\) in the air
• (d) reduce \(CO_2\) and increase \(O_2\) in the air.

Correct Answer: (d)

Explanation: Trees use \(CO_2\) for photosynthesis and release \(O_2\) as a byproduct, helping balance atmospheric gases.

41. Formula of tear gas is:

• (a) \(COCl_2\)
• (b) \(N_2O\)
• (c) \(CCl_3NO_2\)
• (d) none.

Correct Answer: (c)

Explanation: \(CCl_3NO_2\), also known as chloropicrin, is the chemical formula for tear gas.

42. White lung cancer is caused by:

• (a) paper
• (b) textiles
• (c) silica
• (d) asbestos.

Correct Answer: (b)

Explanation: "White lung cancer" (byssinosis) is caused by the inhalation of cotton fibres common in the textile industry.

43. Environmental pollution affects:

• (a) biotic components
• (b) human beings only
• (c) plants only
• (d) biotic and abiotic components of environment.

Correct Answer: (d)

Explanation: Environmental pollution has widespread effects on both living (biotic) and non-living (abiotic) systems.

44. Chlorine in concentration of 0.2 to 0.4 ppm is used as a:

• (a) disinfectant
• (b) detergent
• (c) antiseptic
• (d) antibiotic.

Correct Answer: (a)

Explanation: In small concentrations, chlorine is used as a disinfectant to make water safe for drinking.

45. B.O.D values of samples A (160), B (35), C (180), D (25). Decreasing order of pollution:

• (a) C>A>D>B
• (b) D>B>A>C
• (c) C>A>B>D
• (d) D>A>B>C

Correct Answer: (c)

Explanation: Higher BOD values indicate higher levels of pollution; therefore, the order is C (180) > A (160) > B (35) > D (25).