Explanation

(a)
$HNO_{3}$ (nitric acid) is generally not an amphoteric substance. It is a strong acid (proton-donating) though sometimes, in presence of stronger acid, it also acts as a base (e.g., in nitration of atomic compounds, it acts as a base and accept proton from $H_{2}SO_{4}$). However $HCO_{3}^{-},H_{2}O$ and $NH_{3}$ frequently act both as an acid as well as a base (i.e., amphoteric in nature).