$HC_2H_3O_2(aq)$ 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, $HC_2H_3O_2(aq) \rightleftharpoons H^+(aq) + C_2H_3O_2^-(aq)$ $HC_2H_3O_23$ produces $H^+$ ions in aqueous solutions. So it is an acid.