detailed solution

Correct option is D

The primary component of fuming sulfuric acid is pyrosulfuric acid, a potent acid. It is also referred to as disulfuric acid or oleum, which is a sulphur oxyacid. Compared to sulfuric acid, pyrosulfuric acid is weaker. By interacting with the bases, salts like sodium and potassium pyrosulfates are produced.
The main ingredient in fuming sulfuric acid is pyro sulfuric acid. Pyro sulfuric acid's chemical composition can be written as $H_2{S}_2{O}_7$.