Q1. What does BOD (Biological Oxygen Demand) indicate in water quality testing?
- Amount of bacteria in water
- Total mineral content
- Oxygen required by microorganisms to decompose organic matter
- Level of radioactive pollution
Correct Option: 3. Oxygen required by microorganisms to decompose organic matter
Explanation: BOD is a measure of the amount of dissolved oxygen needed by aerobic biological organisms to break down organic material in water. High BOD = high pollution.
Q2. What is a major consequence of high nitrate levels in drinking water?
- Liver cirrhosis
- Fluorosis
- Skin cancer
- Blue baby syndrome
Correct Option: 4. Blue baby syndrome
Explanation: High nitrate levels can convert hemoglobin into methemoglobin, which cannot carry oxygen effectively, leading to blue baby syndrome in infants.
Q3. Which of the following water pollutants is responsible for “Minamata disease”?
- Arsenic
- Lead
- Mercury
- Cadmium
Correct Option: 3. Mercury
Explanation: Minamata disease was caused by mercury poisoning through consumption of fish contaminated by methyl mercury in Japan’s Minamata Bay.
Q4. What is “Eutrophication”?
- Process of water purification using plants
- Excess nutrients in water leading to algal blooms
- Biological magnification of toxins in food chains
- Process of oil extraction from water
Correct Option: 2. Excess nutrients in water leading to algal blooms
Explanation: Eutrophication results from excess nitrogen and phosphorus in water, which causes algal blooms. This depletes oxygen and harms aquatic life.
Q5. Which method is NOT an effective water pollution control measure?
- Use of water hyacinth to absorb toxins
- Cooling industrial water before discharge
- Dumping untreated sewage into rivers
- Using oil zappers to clean oil spills
Correct Option: 3. Dumping untreated sewage into rivers
Explanation: Dumping untreated sewage is a major source of water pollution, not a control method. Other options are recognized pollution control techniques.