Free Water Pollution and Treatment MCQs with Answers

1. Identify which one of the following water pollutant is Carcinogenic?

• A. Polycyclic hydrocarbons
• B. Mineral acids
• C. D.D.T
• D. Nitrate fertilizers

Explanation: Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds that are formed during incomplete combustion of organic matter, such as fossil fuels, wood, and tobacco. Many PAHs are known or suspected carcinogens, meaning they have the potential to cause cancer in humans. Explanation will be added soon.

2. The disadvantage of use of chlorinated water is:

• A. Formation of NH4Cl , NHCl2 , NCl3 which are eye irritants
• B. Increased risk of bladder and rectal cancer by drinking water
• C. Offensive odour and taste due to chlorinated phenols.
• D. All of the above

Explanation: Disadvantages as advised by CDC guidelines for chlorinated water include following: The drawbacks of chlorination are: Relatively low protection against protozoa Lower disinfection effectiveness in turbid waters Potential taste and odor objections Must ensure quality control of solution Potential long-term effects of chlorination by-products

3. The coagulant used in raw water to precipitate suspended impurities is:

• A. Caustic soda
• B. Lime water
• C. Alum
• D. Soda ash

Explanation: A is incorrect as caustic soda is not used as a coagulant.B is incorrect as lime water is not used as a coagulant,but is used to detect the presence of CO2 gas.C is correct as alum is used as a coagulant in raw water to remove suspended impurities.D is incorrect as soda ash is not used as a coagulant

4. What is the most important source of water pollution in Pakistan?

• A. Industries
• B. Transportation
• C. Mining Industry
• D. Agricultural and municipal wastage

Explanation: Contamination of water bodies is called water pollution. Pakistan is an agricultural country. The root cause of water pollution in Pakistan arises here. The farmers use tons of water for their fields and crops and then dump all the contaminated water into lakes and rivers. In addition to that, the municipal committees are least bothered about the pollution caused by the garbage they throw in the water bodies. The industries also play a role in this, but the formerly mentioned points are the main causes of destruction. Thus, we will go for option D.

5. Water is said to be permanently hard when it contains:

• A. carbonates of Ca2+ and Mg2+ ions
• B. Bicarbonates of Ca2+ and Mg2+ ions
• C. sulphates of Na+ and Mg2+ ions
• D. chlorides of Ca2+ and Mg2+ ions

Explanation: The presence of soluble salts of calcium and magnesium, i.e., sulfates and chlorides of calcium and magnesium, causes permanent hardness in the water.

6. Commonly used coagulant used for the purification of water is:

• A. Ca(NO3)2
• B. MgCl2
• C. Al2(SO4)3
• D. Ca(OH)2

Explanation: In water treatment, coagulants like Al2(SO4)3 (aluminum sulfate) are used to remove impurities by causing them to aggregate for easier removal. This process is essential for removing organic matter, pathogens, and toxic materials. Ca(NO3)2 is a fertilizer, MgCl2 is used for de-icing, and Ca(OH)2 is used for pH adjustment, not as a primary coagulant.

7. Drinking water should be odorless, tasteless and live from turbidity and its pH should range between:

• A. 6.0 to 7.0
• B. 7.0 to 8.5
• C. 4.5 to 6.0
• D. 8.5 to 9.0

Explanation: It is recommended that the pH of drinking water should be between 6.5-8.5 on a scale that ranges from 0 - 14, hence the answer will be B.

8. The presence of microorganisms in drinking water is determined by:

• A. COD
• B. TOC
• C. BOD
• D. TDS

Explanation: Biochemical oxygen demand (BOD) is a chemical procedure for determining the amount of dissolved oxygen needed by microorganisms in a body of water to break down organic material present in a given water sample at a certain temperature over a specific period. The greater the value of BOD, the more rapidly oxygen is depleted in water bodies. This means less oxygen is available to higher forms of aquatic life.

9. Amongst the following, which compounds control the tooth decay:

• A. An Iodide compound
• B. A bromide compound
• C. A chloride compound
• D. A fluoride compound

Explanation: Fluoride is a compound that helps prevent tooth decay by strengthening tooth enamel and making it more resistant to acid attacks from bacteria. It can be found in toothpaste, mouthwash, and even in some drinking water sources. Fluoride ions replace hydroxide ions in the enamel, forming a more stable compound that is less susceptible to decay. Iodide, chloride, and bromide are not as effective in preventing tooth decay as fluoride.

10. COD of water is checked by:

• A. By adding bacteria to the water
• B. Adding chemical oxidizing agent
• C. Both (A) and (B)
• D. None of the above

Explanation: To check the Chemical Oxygen Demand (COD) of water, you typically add bacteria and an oxidizing agent to the water sample. The bacteria help break down the organic matter in the water, while the oxidizing agent helps determine the amount of oxygen required for the oxidation process. By measuring the amount of oxygen consumed, you can determine the COD of the water sample.