Free Environmental Chemistry MCQs with Answers

21. Ozone hole refers to

• A. Hole in ozone layers
• B. Reduction in thickness of ozone layer in stratosphere
• C. Reduction of thickness of ozone in troposphere
• D. Increase concentration of ozone

Explanation: The term "ozone hole" refers to a significant reduction in the thickness or concentration of ozone in the stratosphere, particularly over the polar regions. This phenomenon is most notable over Antarctica, where the ozone layer has been observed to thin significantly during certain periods.

22. The anti freezing agent used in the radiator of an automobile is

• A. Ethanol
• B. Mixture of KNO3 and NaNO3
• C. Ethylene glycol
• D. Benzene

Explanation: Ethylene glycol is commonly used as an antifreeze agent in the radiator of automobiles. It is added to the water in the radiator to lower its freezing point and raise its boiling point, thus preventing the engine coolant from freezing in cold temperatures and boiling in hot temperatures. Ethylene glycol is preferred due to its effectiveness, low cost, and relatively low toxicity compared to alternatives like methanol.

23. The activity of an enzyme is greatly enhanced by the presence of

• A. A co-enzyme
• B. An activator
• C. Apoenzyme
• D. Both (a) and (b)

Explanation: a) A coenzyme: Coenzymes are organic molecules that are required by certain enzymes to carry out catalysis effectively. They often participate in enzyme-substrate interactions and assist in the conversion of substrates into products. Examples of coenzymes include NAD+, FAD, and coenzyme A. By providing chemical groups that the enzyme itself lacks, coenzymes can significantly enhance the activity of enzymes.(b) An activator: Activators are molecules that bind to enzymes and increase their catalytic activity. They can either increase the affinity of the enzyme for its substrate or stabilize the active conformation of the enzyme. Activators can be metal ions (e.g., Mg2+, Ca2+), small organic molecules, or other proteins. By binding to the enzyme, activators help in facilitating the enzyme-substrate interaction and promote the conversion of substrates into products.

24. The gas which reacts with haemoglobin by displacing oxygen is:

• A. Carbon monoxide
• B. Sulfur dioxide
• C. Carbon dioxide
• D. Methane

Explanation: Carbon monoxide (CO) has an affinity for haemoglobin that is over 200 times greater than that of oxygen. When inhaled, it binds tightly to haemoglobin to form carboxyhaemoglobin, which prevents the transport of oxygen in the blood.

25. The ozone layer that absorbs the sun's ultraviolet radiation is present in _ layer of atmosphere.

• A. Thermosphere
• B. Mesosphere
• C. Stratosphere
• D. Troposphere

Explanation: The vast majority of atmospheric ozone (O3) is found in the stratosphere, a layer extending from about 10 to 50 km above the Earth's surface. This ozone layer is crucial for absorbing most of the biologically harmful ultraviolet (UV) radiation from the sun.

26. The BOD value of clean water is:

• A. < 5 ppm
• B. < 15 ppm
• C. > 15 ppm
• D. > 17 ppm

Explanation: Biochemical Oxygen Demand (BOD) is a measure of the amount of oxygen required by aerobic bacteria to decompose organic waste in water. Clean, unpolluted water has a very low amount of organic waste, resulting in a low BOD value, typically less than 5 ppm.

27. Choose the factor that is primarily responsible for ozone layer depletion:

• A. CFCs
• B. CBrCs
• C. CH2Br2
• D. All are correct

Explanation: Chlorofluorocarbons (CFCs) are highly stable compounds that, when they reach the stratosphere, are broken down by UV radiation to release chlorine free radicals. These radicals catalytically destroy ozone molecules, leading to the depletion of the ozone layer.

28. Select the major air pollutant:

• A. CO
• B. Mist
• C. Hydrogen sulphide
• D. All are correct

Explanation: Air pollution is caused by a variety of substances. Carbon monoxide (CO) is a major gaseous pollutant, while mist is a particulate pollutant. Hydrogen sulphide is another toxic gas. All of these contribute to air pollution.

29. Besides carbondioxide and nitrous oxide, another significant greenhouse gas is:

• A. Methane
• B. Carbon monoxide
• C. Both a and b
• D. None of these

Explanation: Greenhouse gases are those that absorb and emit infrared radiation, trapping heat in the atmosphere. Methane (CH4) is a potent greenhouse gas, along with carbon dioxide, nitrous oxide, and water vapor. Carbon monoxide is not a significant greenhouse gas.

30. All oxides of Nitrogen are common pollutants except _.

• A. NO2
• B. N2O5
• C. NO
• D. N2O

Explanation: Nitrogen oxides like NO and NO2 (collectively known as NOx) and nitrous oxide (N2O) are significant air pollutants and/or greenhouse gases. Dinitrogen pentoxide (N2O5) is a highly reactive and unstable solid that readily reacts with water to form nitric acid and is not typically considered a primary atmospheric pollutant itself.