Free Environmental Chemistry MCQs with Answers

131. Unpolluted rain water has a pH of:

• A. 4.9
• B. 5.6
• C. 5.3
• D. 7.0

Explanation: The correct answer is 5.6. Unpolluted rainwater is slightly acidic due to the formation of carbonic acid, which occurs when carbon dioxide in the atmosphere dissolves in rainwater. This process results in a pH of approximately 5.6. Option A (4.9) represents a more acidic condition that would not be typical for natural rainwater unless affected by additional pollutants. Option C (5.3) is closer but still more acidic than the average for unpolluted conditions. Finally, Option D (7.0) indicates a neutral pH, which does not account for the natural acidity introduced by carbonic acid.

132. Anaerobic decomposition of organic matter i.e. glucose by bacteria in water sediments produces?

• A. Propene
• B. Ethane
• C. Methane
• D. Butane

Explanation: One natural source of methane is the anaerobic decomposition of organic matter by bacteria in water sediments and in soils.

133. The yellowish-brown color in photochemical smog is due to the presence of:

• A. Sulphur dioxide
• B. Carbon monoxide
• C. Carbon dioxide
• D. Nitrogen dioxide

Explanation: The yellow colour in photochemical smog is due to the presence of nitrogen dioxide.

134. Ozone concentration is measured in:

• A. Debye units
• B. Dupont units
• C. Debacle units
• D. Dobson units

Explanation: The Dobson unit is the correct unit for measuring ozone concentration. It is named after G.M.B. Dobson, who was a British meteorologist. Dobson units represent the thickness of an ozone layer if it were condensed into a single layer at standard temperature and pressure (STP).

135. The gas that is mainly produced in landfills from the waste is:

• A. CH4
• B. CO2
• C. SO2
• D. Cl2

Explanation: Methane is the gas released from marshy and landfill areas. Methane is released as waste material by bacteria.In landfill areas, gases are produced when bacteria break down organic waste. it includes mainly CO2 and methane, and traces of some other gases like nitrogen, Oxygen and ammonia, but the byproduct in that case is always methane.

136. The substance for the separation of isotopes is first converted into the:

• A. Neutral state
• B. Free state
• C. Vapour state
• D. Charged state

Explanation: Mass spectrometry is one of the most precise ways of differentiating isotopes on the bases of charge-to-mass ratio It includes five major STEPS IN the following sequence: (1) Vaporization: the sample of the element is vaporized. (2) Ionization-positive ions are obtained from the vapour (3) Acceleration: the positive ions are accelerated by an electric field (4) Deflections are deflected by magnetic fields. (5) Detection-ions are detected and the record is made

137. Photochemical smog is primarily caused by:

• A. O3
• B. NO2
• C. SO3
• D. CO2

Explanation: Photochemical smog appears to be initiated by nitrogen oxides that are emitted into the air as pollutants mainly from internal combustion engines. Absorbing the visible or ultraviolet energy of sunlight, it forms nitric oxide (NO) to free atoms of oxygen (O), which then combine with molecular oxygen (O2) to form ozone (O3). In the presence of hydrocarbons (other than methane), certain other organic compounds, and sunlight, various chemical reactions take place to form photochemical smog.

138. Which of the following pollutant decolorizes the skin?

• A. Mercury
• B. Arsenic
• C. Lead
• D. Cadmium

Explanation: Air pollutants damage the skin by inducing oxidative stress. Although human skin acts as a biological shield against pro-oxidative chemicals and physical air pollutants, prolonged or repetitive exposure to high levels of these pollutants may have profound negative effects on the skin.

139. If CO2 level increase from the normal level, what will happen?

• A. Decrease in sea level
• B. Increase in sea level
• C. Longer winter season
• D. Daytime will increase

Explanation: If CO2 level increases than normal as the world warms due to greenhouse gases carbon dioxide included waters heat up and expand, causing sea levels to rise. The researchers found that the natural relationship displays a strong rise in sea level for CO2 increase from 180 to 400 parts per million, peaking at CO2 levels close to present-day values. The increased percentage of carbon-dioxide will cause the greenhouse effect, i.e. it will not allow the hot rays of the sun to escape from the atmosphere after reflection once they enter the earth's atmosphere, thereby increasing the temperature of the earth, ice on mountains will melt and the water level will rise.

140. As a result of increased CO2 in the atmosphere, oceans will become more:

• A. Alkaline
• B. Acidic
• C. Saline
• D. Cooler

Explanation: Because of human-driven increased levels of carbon dioxide in the atmosphere, there is more CO2 dissolving into the ocean. The ocean's average pH is now around 8.1 , which is basic (or alkaline), but as the ocean continues to absorb more CO2, the pH decreases and the ocean becomes more acidic.