Question

Which air pollutant is mainly responsible for acid rain?

• A. CO and CO$_2$
• B. NO$_2$ and SO$_2$
• C. O$_3$ and PAN
• D. NH$_3$ and CH$_4$

Hint:

Acid rain is always linked with {SO$_2$ and NO$_x$}. Remember: sulphuric and nitric acids are the culprits.

Answer 1

The Correct Option is B

To determine which air pollutants are mainly responsible for acid rain, we need to understand the chemical processes involved in its formation.

Acid rain is primarily caused by the emissions of sulfur dioxide (SO₂) and nitrogen dioxide (NO₂) into the atmosphere. These gases are produced from burning fossil fuels like coal, oil, and natural gas, as well as from industrial processes and vehicle emissions.

1. Sulfur Dioxide (SO₂): This gas reacts with oxygen to form sulfur trioxide (SO₃), which further combines with water vapor in the atmosphere, forming sulfuric acid (H₂SO₄).

The chemical reaction is shown below:

\(2SO_2 + O_2 \rightarrow 2SO_3\)

\(SO_3 + H_2O \rightarrow H_2SO_4\)

1. Nitrogen Dioxide (NO₂): This gas reacts with water to form nitric acid (HNO₃).

The chemical reaction is:

\(4NO_2 + 2H_2O + O_2 \rightarrow 4HNO_3\)

Hence, the formation of sulfuric acid and nitric acid contributes to the acidity of rain. As acid rain falls on the ground, it can have harmful impacts on aquatic life, plants, and infrastructure.

Now, let's examine the provided options:

1. CO and CO₂: Carbon monoxide (CO) and carbon dioxide (CO₂) are not significantly involved in acid rain formation. These gases contribute to other environmental issues such as global warming and air pollution but not acid rain.
2. NO₂ and SO₂: As explained above, these are the primary pollutants responsible for acid rain.
3. O₃ and PAN: Ozone (O₃) and peroxyacetyl nitrate (PAN) are secondary pollutants involved in photochemical smog and not acid rain.
4. NH₃ and CH₄: Ammonia (NH₃) and methane (CH₄) do not play a significant role in acid rain. They contribute to other phenomena like the greenhouse effect and eutrophication.

Therefore, the correct answer is NO₂ and SO₂, as they are the main pollutants responsible for acid rain formation.

Answer 2

Step 1: Understanding acid rain.
Acid rain refers to precipitation such as rain, snow, or fog that contains strong acidic components. These acids are mainly sulfuric acid (H$_2$SO$_4$) and nitric acid (HNO$_3$), which are formed due to chemical reactions of certain air pollutants in the atmosphere.
Step 2: Formation mechanism of acid rain.
Sulphur dioxide (SO$_2$) and nitrogen dioxide (NO$_2$) are released into the atmosphere from burning fossil fuels, industrial processes, and vehicle emissions. These gases react with oxygen, water vapor, and oxidizing agents in the atmosphere to form sulfuric acid and nitric acid.
Step 3: Analysis of options.
(A) CO and CO$_2$: Carbon monoxide is toxic, and carbon dioxide causes global warming, but neither directly forms strong acids responsible for acid rain.
(B) NO$_2$ and SO$_2$: Correct — These gases are the primary precursors of nitric acid and sulfuric acid, which cause acid rain.
(C) O$_3$ and PAN: These are components of photochemical smog, not acid rain.
(D) NH$_3$ and CH$_4$: Ammonia can neutralize acids, and methane is mainly a greenhouse gas.
Step 4: Final conclusion.
Since sulphur dioxide and nitrogen dioxide directly form strong acids in the atmosphere, the correct answer is (B) NO$_2$ and SO$_2$.