Carbon monoxide is a _____ (basic/neutral) oxide.

Neutral oxides:

• Neutral oxides are those which when reacted with water display neither the acidic characteristics nor the basic one.
• Their solutions are neutral and they do not form salts when reacted with acids or bases, e.g., Carbon monoxide ($\mathbf{CO}$), Nitrous oxide (${\mathbf{N}}_{\mathbf{2}}\mathbf{O}$) etc.

Thus, carbon monoxide is a neutral oxide.