Answer: D. Lowering of pH of soil
Suplhur dioxide is released into the atmosphere from a number of
sources. In the atmosphere, sulphur dioxide reacts with atmospheric
oxygen to form sulphur trioxide by photolytic and catalytic oxidation
processes. The suplhur trioxide thus formed reacts with water, producing
sulphuric acid. This acid is washed down on earth as acid rain.
Thus, the purest form of rain reaches the earth as an acidic solution of pH.