Free Environmental Chemistry MCQs with Answers

31. Acid rain is due to:

• A. Formation of oxides of sulphur
• B. Formation of oxides of nitrogen
• C. Formation of H2SO4 and HNO3
• D. All of these

Explanation: Acid rain is primarily caused by the emission of sulfur dioxide (SO2) and nitrogen oxides (NOx) into the atmosphere. These gases react with water, oxygen, and other chemicals to form sulfuric acid (H2SO4) and nitric acid (HNO3), which then fall to the earth as acid rain.

32. BOD is a measure of:

• A. Organic pollutants in water
• B. Oxides of SPN in air
• C. Inorganic pollutant in water
• D. Particle matter in water

Explanation: Biochemical Oxygen Demand (BOD) indirectly measures the amount of biodegradable organic pollutants in a water sample. A higher BOD indicates a greater amount of organic pollution, as more oxygen is required for its microbial decomposition.

33. Which is not a natural source of air pollution?

• A. Forest fire
• B. Coal fire
• C. Volcanoes
• D. Dust storm

Explanation: While forest fires, volcanic eruptions, and dust storms are all natural events that release pollutants into the atmosphere, the burning of coal is an anthropogenic (human-caused) activity and is not a natural source of pollution.

34. The layer that protects us from harmful U.V. radiation is:

• A. CO2
• B. O3
• C. NO2
• D. O2

Explanation: The ozone (O3) layer, located in the stratosphere, plays a critical role in absorbing the majority of the sun's high-frequency ultraviolet (UV) radiation. This absorption protects life on Earth from the harmful effects of UV exposure.

35. Choose the process that is not the reason of increase of CO2 concentration in atmosphere.

• A. Decay of animals
• B. Respiration
• C. Photosynthesis
• D. Burning of petrol

Explanation: Photosynthesis is the process by which plants and other organisms use sunlight to convert carbon dioxide and water into glucose and oxygen. This process consumes CO2 from the atmosphere, thereby reducing its concentration, unlike the other processes which release CO2.

36. _ is a secondary pollutant.

• A. CO
• B. CO2
• C. PAN
• D. NO2

Explanation: A secondary pollutant is not emitted directly but forms in the atmosphere when primary pollutants react. Peroxyacetyl nitrate (PAN) is a key component of photochemical smog, formed from the reaction of hydrocarbons and nitrogen oxides in the presence of sunlight.

37. DDT is a/an:

• A. Biodegradable pollutant
• B. Non-biodegradable pollutant
• C. Insecticide
• D. Both options B and C are correct

Explanation: DDT (Dichlorodiphenyltrichloroethane) is a synthetic chemical that was widely used as an insecticide. It is also a persistent organic pollutant because it is not easily broken down by environmental processes, making it non-biodegradable.

38. The ozone layer needs protection against the indiscriminate use of _.

• A. Fungicides, insecticides, bactericides, and medicines
• B. Refrigerants and high-flying jets
• C. Atomic explosions and industrial wastes
• D. None of these

Explanation: Many common refrigerants and aerosol propellants are chlorofluorocarbons (CFCs), which are the primary cause of ozone depletion. Additionally, the exhaust from high-flying jet aircraft can release nitrogen oxides directly into the stratosphere, which also contributes to ozone destruction.

39. Mottling of teeth caused by the excessive intake of _.

• A. Potassium
• B. Iodine
• C. Chlorine
• D. Fluorine

Explanation: Dental fluorosis, which in its more severe forms causes a "mottled" or stained appearance of the tooth enamel, is a condition caused by the excessive intake of fluoride during the years when teeth are developing.

40. Photochemical smog is a secondary pollutant and it is generally formed:

• A. In the morning of winters
• B. Around mid-day in summer months
• C. On a rainy day
• D. When the concentration of particulate matter is very low

Explanation: Photochemical smog formation requires sunlight to initiate the reactions between primary pollutants like nitrogen oxides and volatile organic compounds. These conditions are most prevalent on sunny, warm, dry days, typically during the summer months around midday when sunlight is most intense.