Based on their acid-base characteristics oxides are classified as acidic or basic. 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.

${\mathrm{P}}_4{\mathrm{O}}_{10},{ \mathrm{B}}_2{\mathrm{O}}_3,{ \mathrm{N}}_2{\mathrm{O}}_5, {\mathrm{SO}}_3$ are acidic oxides.

$\mathrm{NO}, {\mathrm{N}}_2\mathrm{O}, \mathrm{CO}$ are neutral oxides.