Consider the following:

1. Carbon monoxide

2. Nitrogen oxide

3. Ozone

4. Sulphur dioxide

Excess of which of the above in the environment is/are cause(s) of acid rain?

The correct answer is 2 and 4 only.

Key PointsAcid Rain:

• The term ‘acid rain’ refers to the deposition of wet or dry acidic materials from the atmosphere on the earth’s surface.
• Although most conspicuously associated with rainfall, the pollutants may fall on the earth’s surface either in the form of snow, sleet, hail, or fog or in the dry form of gases or particulate matter.
• Smokes emitted from the industries are the major source of sulfur dioxide whereas smoke emitted from the motor vehicle is the major source of nitrogen oxide. Hence only 2 and 4 are correct.
• Ozone is a highly reactive gas and a major component of smog. However, it does not directly cause acid rain. Ozone is more related to air quality and respiratory problems, but it doesn’t lead to the formation of acidic compounds in the rain. Hence, Option 3 is incorrect. 
• Carbon monoxide is a colorless, odorless gas produced by the incomplete combustion of carbon-containing fuels (like gasoline or coal). While CO is a pollutant and harmful to health, it does not directly contribute to acid rain because it doesn't form acidic compounds when it reacts in the atmosphere. Hence, Option 1 is incorrect. 

Sources of compounds causing acid rain:

• Sulfur:
  • Natural Resources: - Seas and oceans, Volcanic eruptions, Biological processes in the soil e.g., Decomposition of Organic matter
  • Man-made sources: - Burning of coal (60%), Petroleum products (30 % of S02) and smelting of metal sulfides ores to obtain the pure metals, Industrial production of sulphuric acid in metallurgical, chemical, and fertilizers industries.
• Nitrogen:
  • Natural Resources: - Lightning, Volcanic eruptions
  • Anthropogenic sources: - Forest fires, Combustion of Oil, Coal, And Gas

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