Answer
a) $SO_{3}$
b) $ZnO$
c) $CaO$
Work Step by Step
a) $SO_{3}$ is an acidic oxide because it can react with bases, for example: $SO_{3} + 2NaOH \rightarrow Na_{2}SO_{4} + H_{2}O$
b) $ZnO$ is an amphoteric oxide because it can react both with bases and acids, for example:
$ZnO + 2NaOH \rightarrow Na_{2}ZnO_{2} + H_{2}O$
$ZnO + 2HCl \rightarrow ZnCl_{2} + H_{2}O$
c) $CaO$ is a basic oxide because it can react with acids, for example: $CaO + 2HCl \rightarrow CaCl_{2} + H_{2}O$
