Free Environmental Chemistry MCQs with Answers

171. 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. In rainy day
• D. When concentration of particulate matter is very low

Explanation: To form Photochemical smog, the presence of sunlight (high temperature) requires when nitrogen oxide reacts with volatile organic compounds.

172. Which one is not included under greenhouse gases?

• A. CO
• B. CH4
• C. Chlorofluorocarbons
• D. SO2

Explanation: Greenhouse gases are carbondioxide, nitrous oxide, methane, carbon monoxide, water vapours and CFCs (chlorofluorocarbons).

173. Choose the compound that is always present in photochemical smog:

• A. O3
• B. CO
• C. CO2
• D. CHO

Explanation: During the formation of photochemical smog, NO2 breaks into NO, and O. O reacts with O2 producing O3, hence O3 is always present in photochemical smog.

174. Phosphate pollution is caused by :

• A. Weathering of phosphate rocks only
• B. Agricultural fertilizers
• C. Phosphate rocks and sewage
• D. Sewage and agricultural fertilizers

Explanation: Phosphate pollution occurs by Sewage and agricultural fertilizers. Algal blooms occurs when phosphate in large amount enters in water bodies therefore sunlight does not reach to the aquatic animals and plants which leads to their death.

175. Choose the correct statement:

• A. Ultraviolet radiation from sun causes a reaction that produces ozone
• B. Ozone hole is depletion in total amount of O
• C. A single chlorine free radical can destroy 10000 ozone molecules
• D. AII of above

Explanation: Ultraviolet radiations cause photochemical splitting of oxygen molecules in the stratosphere. The nascent oxygen combines with molecular oxygen to form ozone. In troposphere nascent oxygen comes from nitrogen dioxide. Option B is incorrect because ozone depletion does not reduce the amount of oxygen atoms, however it reduces the amount of ozone (O3) by converting it to oxygen gas O2. Option C is incorrect because a single chloride free radical can destroy upto 100,000 ozone molecules.

176. Which of the following is not an air pollutant?

• A. N2
• B. N2O
• C. NO
• D. CO

Explanation: Nitrogen is an inert gas - meaning it doesn't chemically react with other gases - and it isn't toxic

177. Natural rain forms _ in the presence of carbon dioxide in the air.

• A. Smog
• B. Ozone
• C. Carbonic acid
• D. Chlorofluorocarbons

Explanation: CO2+H2O->H2CO3 This is how carbonic acid is formed from water.

178. The major source of unburnt hydrocarbons in the atmosphere is/are:

• A. Petroleum
• B. Natural gas
• C. Automobiles
• D. Human beings

Explanation: There are many sources of unburned hydrocarbons. Unburned hydrocarbons (UHC) are typically an output of incomplete combustion due to unfavorable engine design, low fuel quality, or failure in the control system. Sometimes unburned hydrocarbons are released into the air during incomplete combustion. Burning fossil fuels, including gasoline in automobile engines, releases some hydrocarbons into the air. In a typical urban environment, the atmospheric concentration of hydrocarbons is around 3 ppm (parts per million).

179. Coal contain sulphur:

• A. 1 - 3 %
• B. 2 - 5 %
• C. 1 - 9 %
• D. 3 - 8 %

Explanation: Organic sulfur is chemically bonded to the carbon atoms in the coal. The organic sulfur content of most coals ranges from 0.5% to about 2%.

180. What is the most common gas in the environment?

• A. N2
• B. CO2
• C. O2
• D. He

Explanation: The most abundant naturally occurring gas is nitrogen (N2), which makes up about 78% of air. Oxygen (O2) is the second most abundant gas at about 21%. The inert gas argon (Ar) is the third most abundant gas at 0.93%.