Concept:Drying agents are chosen based on the chemical nature of the gas or substance to be dried.
Explanation:Concentrated tetraoxosulphate(VI) acid,
H2SO4, is an acidic drying agent.
Calcium oxide,
CaO, is a basic drying agent.
Acid anhydrides react with bases like calcium oxide, so they cannot be dried using
CaO.
Acid anhydrides do not react with concentrated
H2SO4, so they can be dried with it.
Hence, the compound is an acid anhydride.
Answer:D. an acid anhydride