Free Environmental Chemistry MCQs with Answers

161. In the purification of portable water, the coagulant used is?

• A. alum
• B. BOD
• C. COD
• D. All of the above

Explanation: Alum, or aluminum sulfate, is commonly used as a coagulant in the purification of portable water. When added to water, alum forms a gelatinous precipitate called floc, which traps impurities such as suspended particles, dirt, and microorganisms. These impurities settle to the bottom of the water, allowing for easier removal during the filtration process. Therefore, option (a) is correct. Now we'll look at why other options are incorrect.(b) BOD (Biochemical Oxygen Demand): BOD is not a coagulant used in the purification of portable water. Instead, BOD is a measure of the amount of dissolved oxygen consumed by microorganisms during the decomposition of organic matter in water. It is used as an indicator of water quality and pollution levels but is not directly involved in the purification process. Therefore, option (b) is incorrect.(c) COD (Chemical Oxygen Demand): Similar to BOD, COD is not a coagulant used in the purification of portable water. COD is a measure of the amount of oxygen required to oxidize organic and inorganic compounds in water. It is also used as an indicator of water quality and pollution levels but does not play a role in water purification. Therefore, option (c) is incorrect.(d) All of the above: This option is incorrect because only option (a) (alum) is the correct coagulant used in the purification of portable water. Options (b) and (c) (BOD and COD) are not coagulants and are not directly involved in the purification process.(Environmental chemistry,Solid Waste Management and Water Treatment)

162. Chlorination of water may be harmful if the water contains ?

• A. Ammonia
• B. Dissolved Oxygen
• C. Carbon Dioxide
• D. All

Explanation: Option (d) is correct because chlorination of water containing any of these substances can be harmful due to the formation of disinfection by-products.Now we'll look at why other options are incorrect.(a) Ammonia: Chlorination of water containing ammonia can produce harmful disinfection by-products (DBPs) such as chloramines. Chloramines are less effective disinfectants than free chlorine and can also cause health issues, including respiratory problems and eye irritation.(b) Dissolved Oxygen: Chlorination of water containing dissolved oxygen can lead to the formation of trihalomethanes (THMs) and haloacetic acids (HAAs), which are harmful DBPs. THMs and HAAs are associated with an increased risk of cancer and other health problems.(c) Carbon Dioxide: Chlorination of water containing carbon dioxide can lead to the formation of additional DBPs such as chloroform. Chloroform is a carcinogen and can also cause liver and kidney damage.(Environmental chemistry,Components of Environment)

163. The percentage of suspended solid waste in raw water is removed by coagulation is?

• A. 60
• B. 70
• C. 80
• D. 90

Explanation: In many coagulation processes, achieving an 80% removal of suspended solids from raw water is indeed feasible. Coagulation, along with subsequent processes like flocculation and sedimentation, can effectively remove a significant portion of suspended solids, leading to clearer water. Therefore, option (c) "80" is correct in this context.(Environmental chemistry,Components of Environment)

164. Choose the correct statement:

• A. The human body does not produce enzymes
• B. The human body does not produce vitamins
• C. Proteins are an energy source for our body
• D. Nucleic acids are building blocks for our body

Explanation: With few exceptions, vitamins are essential nutrients that the human body cannot synthesize and must therefore be obtained through diet.

165. Peroxyacetyl nitrate (PAN) is an irritant to human beings and it affects:

• A. Eyes
• B. Ears
• C. Stomach
• D. Nose

Explanation: PANs have many adverse effects in the human body such as reduced respiratory function (including emphysema and impaired breathing) and eye irritation.

166. A single chlorine free radical can destroy how many ozone molecules:

• A. 100
• B. 10,000
• C. 10,00,000
• D. 100,000

Explanation: A single chloride free radical can destroy upto 100,000 ozone molecules.

167. The yellow colour in photochemical smog is due to the presence of:

• A. NO
• B. NO2
• C. SO2
• D. CO2

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

168. The formula of "rock salt" is:

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

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.

169. Bacteria plays an important role in:

• A. Phosphorus Cycle
• B. Nitrogen Cycle
• C. Carbon Cycle
• D. All of these

Explanation: In nitrogen cycle :Nitrogen-fixing bacteria convert N2 to ammoniaNitrifying bacteria convert ammonia to nitrates and nitritesDenitrifying bacteria release the N2 back to the atmosphere by converting nitrates back to atmospheric nitrogenIn the carbon cycle, bacteria decompose dead organisms and release carbon back to the environment.In the phosphorus cycle, bacteria convert phosphate into the organic form so that it can be utilized by the plants.

170. BOD is a measure of:

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

Explanation: BOD is the amount of oxygen needed to decompose the organic material present in the water.