Answer
$HNO_3(aq)$ is an acid according to the Arrhenius definition.
Work Step by Step
According to the Arrhenius definition, an acid is a substance which produces $H^+$ ions in an aqueous solution.
As we can see from the below equation,
$HNO_3(aq) \rightarrow H^+(aq) + NO_3^-(aq)$
$HNO_3$ produces $H^+$ ions in aqueous solutions. So it is an acid.
