Which of the following results in the fall of acid rain?

Analysis

The question asks for the primary pollutant responsible for the phenomenon known as "acid rain." Acid rain occurs when certain gases react with water vapor in the atmosphere to form acidic solutions that fall to the earth.

Concept Explanation

Acid rain is primarily caused by the emission of non-metallic oxides into the atmosphere. When these oxides (specifically oxides of sulphur and nitrogen) react with water ($H_2O$) in the clouds, they form strong acids.

• Sulphur dioxide ($SO_2$): When released from the burning of fossil fuels (like coal and oil), it reacts with oxygen and water in the atmosphere to form sulphuric acid ($H_2SO_4$).
• Nitrogen oxides ($NO_x$): These also contribute to the formation of nitric acid ($HNO_3$).

These acids lower the pH of rainwater, making it acidic, which can damage buildings, harm aquatic life, and degrade soil quality.

Step-by-Step Solution

1. Evaluate Option A (Oxide of lead): Lead oxides are toxic heavy metal pollutants but do not significantly contribute to the acidity of rain.
2. Evaluate Option B (Particulate matter): These are solid or liquid particles suspended in the air (like dust or soot). While they cause air pollution and respiratory issues, they are not the primary chemical cause of acid rain.
3. Evaluate Option C (Oxides of sulphur): Sulphur dioxide ($SO_2$) and sulphur trioxide ($SO_3$) are the main culprits. They dissolve in rainwater to produce sulphurous and sulphuric acids. This is the classic cause of acid rain taught in the chemistry syllabus.
4. Evaluate Option D (Gaseous hydrocarbon): Hydrocarbons contribute to smog and the greenhouse effect, but they do not directly form acids when reacting with water vapor.

Conclusion

Based on the chemical processes involved in atmospheric pollution, oxides of sulphur are the primary agents responsible for the formation of acid rain.

Exam Tip: Whenever you see "Acid Rain" in a JAMB or WASSCE question, immediately look for Oxides of Sulphur ($SO_2$) or Oxides of Nitrogen ($NO_2$). If both are present, they are both correct, but usually, one is provided as the primary answer.