Explanation

(d)
Aqueous solutions of $HCOONa,\ C_{6}H_{5}NH_{3}Cl,KCN$ are basic, acidic and basic in nature.
$HCOONa + H_{2}O \rightleftharpoons HCOOH\ \ \ \ + \ \ NaOH$
Weak acid strong acid
(Basic solution)
$C_{6}H_{5}NH_{3}Cl(aq) \rightleftharpoons C_{6}H_{5}NH_{2}\ \ + \ \ \ \ \ HCl$
Weak base strong acid
(Acidic solution)
$KCN + H_{2}O\ \ \ \ \ \ \ \rightleftharpoons \ \ \ \ \ \ KOH\ \ \ \ \ \ + \ \ \ \ \ HCN$
Strong base weak acid
(Basic solution)