Detailed Explanation:

Answer: Option 2 — 2, 3 and 4 Only

❌ Statement 1 – Incorrect: Carbon dioxide (CO₂) is a greenhouse gas but is NOT included in India's National Air Quality Index (AQI) calculation, which focuses on pollutants with direct health impacts rather than climate change gases.

✅ Statement 2 – Correct: Carbon monoxide (CO) is one of the eight pollutants monitored under the National AQI; it is a toxic gas from incomplete combustion that reduces oxygen transport in blood.

✅ Statement 3 – Correct: Nitrogen dioxide (NO₂) is included in the AQI calculation as a major pollutant from vehicle exhausts and industrial processes that causes respiratory problems.

✅ Statement 4 – Correct: Sulphur dioxide (SO₂) is a criteria pollutant for the AQI, released from burning fossil fuels in power plants and industries.

❌ Statement 5 – Incorrect: Methane (CH₄) is a potent greenhouse gas but is NOT directly measured in the National AQI calculation.

Note: India's National AQI monitors eight pollutants: PM₁₀, PM₂.₅, NO₂, SO₂, CO, O₃, NH₃, and Pb.