Concept:Oxides are classified as acidic, basic, amphoteric, or neutral based on their reaction with acids and bases.
Explanation:SO3 is a non-metal oxide, so it is an acidic oxide.
NO is a non-metal oxide and behaves as a neutral oxide.
Al2O3 reacts with both acids and bases, so it is an amphoteric oxide.
CaO is a metal oxide and is strongly basic in nature.
It reacts with water to form a base:
CaO+H2O→Ca(OH)2.
It also reacts with acids to form salt and water, confirming its basic character.
Hence, the basic oxide among the given options is CaO.
Answer:D. CaO