Question

Which of the following are acid forming precursor gases and causes acid rain?

• A. O\(_3\) and SO\(_2\)
• B. NO\(_2\) and SO\(_2\)
• C. CO\(_2\) and SO\(_2\)
• D. NO\(_2\) and NH\(_3\)

Hint:

Remember the simple chemical associations for acid rain: SO\(_2\) leads to Sulfuric Acid, and NO\(_2\) leads to Nitric Acid. These two acids are the main components of acid rain.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Acid rain is precipitation that is unusually acidic. It is caused when certain precursor gases are released into the atmosphere, where they react with water, oxygen, and other chemicals to form acidic compounds.

Step 3: Detailed Explanation:
The two primary precursor gases responsible for acid rain are:
\[\begin{array}{rl} \bullet & \text{Sulfur dioxide (SO\(_2\)): When SO\(_2\) reacts with water in the atmosphere, it forms sulfurous acid (H\(_2\)SO\(_3\)). Further oxidation can lead to the formation of sulfuric acid (H\(_2\)SO\(_4\)), a very strong acid.} \\ \bullet & \text{Nitrogen oxides (NOx), primarily nitrogen dioxide (NO\(_2\)): When NO\(_2\) reacts with water, it forms nitric acid (HNO\(_3\)) and nitrous acid (HNO\(_2\)), both of which contribute to the acidity of rain.} \\ \end{array}\] While CO\(_2\) does form carbonic acid and makes normal rain slightly acidic (pH ~5.6), it is not considered the cause of the "acid rain" problem, which refers to rain with a much lower pH. O\(_3\) (ozone) is an oxidant that can facilitate the formation of acids but is not a precursor itself. NH\(_3\) (ammonia) is a basic gas.

Step 4: Final Answer:
The primary acid-forming precursor gases that cause acid rain are NO\(_2\) and SO\(_2\).