Answer
a. $HNO_3$ is an acid.
$$HNO_3(aq) \longrightarrow H^+(aq) + N{O_3}^-$$
b. $N{H_4}^{+}$ is an acid.
$$N{H_4}^+(aq) \leftrightharpoons NH_3(aq) + H^+(aq)$$
c. KOH is a base.
$$KOH(aq) \longrightarrow K^+(aq) + OH^-(aq)$$
d. $HC_2H_3O_2$ is an acid.
$$HC_2H_3O_2(aq) \leftrightharpoons H^+(aq) + C_2H_3{O_2}^-(aq)$$
Work Step by Step
1. According to Arrhenius' definition, an acid is a substance that produce $H^+$ ions in aqueous solution. Therefore, they must have a disponible $H^+$ in their structures, like $HNO_3$, $HC_2H_3O_2$ and $NH{_4}^+$.
2. According to the same scientist, bases are substances that produce $OH^-$ ions in aqueous solution. Therefore, they must have a disponible $OH^-$ like $KOH$.
3. The chemical equation is basically the substance ionazing, separating their ions.
