Q1. What is the pH range below which rain is considered “acid rain”?
- Below 6.5
- Below 6.0
- Below 5.6
- Below 7.0
Correct Option: 3. Below 5.6.
Explanation: Normal rain is slightly acidic with a pH around 5.6 due to the natural presence of carbon dioxide. However, when rain has a pH below 5.6, it is classified as acid rain. This increased acidity is primarily caused by the presence of sulfuric and nitric acids formed from SO₂ and NOₓ in the atmosphere.
Q2. Which of the following is a natural source of sulfur oxides?
- Industrial smelting
- Burning of coal
- Car exhausts
- Volcanic eruptions
Correct Option: 4. Volcanic eruptions.
Explanation: While burning coal and industrial smelting are major anthropogenic sources, volcanic eruptions are a significant natural source of sulfur oxides (mainly SO₂). These gases, when released into the atmosphere, can contribute to acid rain formation.
Q3. Which pollutant is primarily responsible for the corrosion of buildings due to acid rain?
- Ozone
- Carbon monoxide
- Sulfur dioxide
- Methane
Correct Option: 3. Sulfur dioxide.
Explanation: Sulfur dioxide (SO₂) reacts with water vapor and oxygen in the atmosphere to form sulfuric acid, which contributes to acid rain. When acid rain falls on buildings—especially those made of limestone or marble—it reacts chemically with the surface, leading to corrosion and damage over time.
Q4. What role do lichens play in detecting air pollution?
- Neutralize acid rain
- Act as bio-indicators
- Absorb heavy metals from air
- Produce oxygen in polluted areas
Correct Option: 2. Act as bio-indicators
Explanation: Lichens are extremely sensitive to air pollutants, especially sulfur dioxide. Because they cannot survive in polluted air, their presence or absence indicates air quality. Hence, they are widely used as bio-indicators of air pollution.
Q5. Which of the following is used in buffering acidified water bodies?
- Sodium chloride
- Calcium oxide or calcium carbonate
- Ammonia
- Hydrogen peroxide
Correct Option: 2. Calcium oxide or calcium carbonate
Explanation: To neutralize acidified lakes or soils, substances like lime (calcium oxide) or limestone (calcium carbonate) are added. These substances increase the pH and restore the natural buffering capacity of water bodies or soil affected by acid rain.