Calcium oxide is used as a drying agent because of its property called .

The correct option is B hygroscopy
$CaO$ is hygroscopic in nature, it absorbs water molecules from nearby regions and keeps the region dry. Thus, it is used as a drying agent.
Hygroscopy is the property by which certain salts absorb moisture from the atmosphere to form hydrated salts.

Efflorescence is the property by which a hydrated substance loses water molecules upon standing in air. It is the opposite of hygroscopy.

Deliquescence is the process by which a substance absorbs moisture from the atmosphere until it dissolves in the absorbed water and forms a solution.