(a) CaO, NO2, SO2, SO3, ZnO
(b) An oxide that combines with water to give an acid is termed as an acidic oxide. The oxide that gives a base in water is known as a basic oxide.
(c) Basic oxide: CaO
Acidic oxides: NO2, SO2, SO3.
Amphoteric oxides: which shows both basic as well as acidic properties, example: ZnO.