Free Environmental Chemistry MCQs with Answers

41. The formula of "rock salt" is:

• A. NaCl
• B. NaHCO3
• C. Na2CO3
• D. CuSO4

Explanation: Halite more commonly known as Rock salt is a mineral formed from sodium chloride. Its chemical formula is NaCl and this also includes other variations of salt such as common salt and table salt.

42. U.V. radiation reacts with oxygen in the atmosphere and produces:

• A. CFC
• B. Carbon dioxide
• C. Sulphur dioxide
• D. Ozone

Explanation: In the stratosphere, high-energy UV radiation breaks the double bond in oxygen molecules (O2), forming two separate oxygen atoms. These highly reactive atoms can then combine with other oxygen molecules to form ozone (O3).

43. Chlorofluorocarbons (CFCs) are important compounds that are used as refrigerants but these are also responsible for ozone layer depletion. If a chlorofluorocarbon CFCl3 is present in stratosphere, which of its reaction intermediates are actually responsible for the breakdown of the ozone molecule?

• A. CFCl2* and Cl*
• B. Cl* and ClO*
• C. CFCl2* and ClO*
• D. CFCl2 and CFCl3

Explanation: In the stratosphere, when a chlorofluorocarbon (CFC) like CFCl3 (also known as CFC-11) is exposed to ultraviolet (UV) radiation, it breaks down into chlorine radicals (Cl*) and a CFCl2 radical. These chlorine radicals (Cl*) are highly reactive and can catalyze the breakdown of ozone (O3) molecules into oxygen (O2). This catalytic cycle involving Cl* and ClO* (chlorine monoxide radical) is responsible for the depletion of the ozone layer.

44. Summer smog is caused primarily by:

• A. PAN
• B. CO2
• C. Ozone
• D. NO2

Explanation: Summer smog, or photochemical smog, is a complex mixture of pollutants. The primary component and indicator of this type of smog is ground-level ozone (O3), which is formed by chemical reactions between oxides of nitrogen and volatile organic compounds in the presence of sunlight.

45. The disease that occurs due to eating fish with high Hg content is:

• A. Minimata disease
• B. Beri-beri disorder
• C. Kwashiorkar disease
• D. Osteosclerosis

Explanation: Minamata disease is a neurological syndrome caused by severe mercury poisoning, first identified in Japan as a result of eating fish and shellfish contaminated with methylmercury from industrial waste.

46. The percentage of CO2 in the atmosphere is:

• A. 0.0042%
• B. 0.042%
• C. 4.2%
• D. 42%

Explanation: The concentration of carbon dioxide in the Earth's atmosphere is a small but significant fraction. As of the early 2020s, the concentration is over 400 parts per million (ppm), which is equivalent to approximately 0.042%.

47. The pollutant _ is formed by the burning of fossil fuels.

• A. Nitrogen dioxide
• B. Nitric acid
• C. Nitrous oxide
• D. Sulphur dioxide

Explanation: Fossil fuels, particularly coal and oil, naturally contain varying amounts of sulphur. When these fuels are burned, the sulphur combines with oxygen from the air to produce sulfur dioxide (SO2), a major air pollutant.

48. The cause of the stratosphere's ozone layer depletion is primarily:

• A. CF2Cl2
• B. C6F6
• C. C6H6F6
• D. C6Cl6

Explanation: Dichlorodifluoromethane (CF2Cl2), also known as Freon-12, is a type of chlorofluorocarbon (CFC). CFCs are the main cause of ozone depletion because they release chlorine atoms in the stratosphere, which catalytically destroy ozone.

49. Which compound is not included under the main list of criteria for air pollutants?

• A. NO2
• B. CO2
• C. O3
• D. SO2

Explanation: While carbon dioxide (CO2) is a major greenhouse gas and a significant factor in climate change, it is not regulated as a "criteria" air pollutant in the same way as pollutants like NO2, ground-level O3, and SO2, which have more direct, immediate health effects.

50. The disease resulting due to depletion of ozone layer is:

• A. Thyroid cancer
• B. Pulmonary cancer
• C. Skin cancer
• D. Breast cancer

Explanation: Depletion of the ozone layer allows more harmful ultraviolet (UV-B) radiation to reach the Earth's surface. Increased exposure to UV-B radiation is a primary cause of skin cancer, including melanoma.