Assertion (A): Coal based thermal power stations contribute to acid rain. Reason (R): Oxides of carbon are emitted when the coal burns.

Assertion (A) is true. Coal contains sulfur and nitrogen impurities. When coal burns in thermal power stations, it releases sulfur dioxide (SO2) and nitrogen oxides (NOx) into the atmosphere. These gases react with water, oxygen, and other chemicals to form sulfuric acid and nitric acid, which are the primary components of acid rain. Reason (R) is true. Coal is mainly carbon, and its combustion produces carbon dioxide (CO2) and, in cases of incomplete combustion, carbon monoxide (CO). Both CO2 and CO are oxides of carbon. However, Reason (R) is not the correct explanation for Assertion (A). While oxides of carbon like CO2 are emitted and contribute to global warming, they are not the primary cause of acid rain. Acid rain is predominantly caused by sulfur dioxide and nitrogen oxides, not oxides of carbon. Carbon dioxide dissolves in rainwater to form carbonic acid, which makes natural rain slightly acidic (pH around 5.6), but this is distinct from the much stronger acidity of acid rain caused by SO2 and NOx. Therefore, both A and R are individually true, but R does not explain A.