Sulphur dioxide is one of the components of polluted air. SO₂ is also a major contributor to acid rain. The correct and complete reaction to represent acid rain caused by SO₂ is :

Solution

Chemistry ma’am · 4 steps

Acid rain means acid in the rain, so the full equation must take SO2 all the way to H2SO4 in water.

1. What acid rain needs. Rain turns acidic when SO₂ ends up as sulphuric acid dissolved in water droplets. So a complete equation must start from SO₂ and finish at H₂SO₄, using what the atmosphere actually supplies: oxygen and water vapour.
2. Two stages. First, SO₂ is oxidised by air (helped by particulate matter): 2SO₂ + O₂ → 2SO₃. Then SO₃ dissolves in water: SO₃ + H₂O → H₂SO₄.

   2SO₂ + O₂ + 2H₂O → 2H₂SO₄

3. Check the balance. Double the second stage and add it to the first. SO₃ cancels. Each side then has 2 S, 4 H and 8 O, so the overall equation is balanced.
4. So. Only (d) shows the whole process, from SO₂ to H₂SO₄ with O₂ and H₂O, so (d) is the answer.

The idea to keep. For acid rain, always write the overall equation ending in the acid: SO₂ goes to H₂SO₄, and NO₂ goes to HNO₃. A step that only makes an oxide is incomplete.

Answer from the NTA final answer key. Solution by PrepWiser.