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 ?

Acid rain is primarily caused by Nitrogen oxides ($NO_x$) and Sulphur dioxide ($SO_2$) reacting with atmospheric water and oxygen to form nitric and sulfuric acids, making option (b) correct. While Carbon monoxide and Ozone are significant air pollutants, they do not directly contribute to the acidification of precipitation, which is why options including them are incorrect. The core concept being tested is the specific chemical precursors of acid rain and their interaction with the hydrological cycle.