Which of the following salts is $NOT$ derived from a weak acid and a weak base?

When a solution of $NH_4Cl$ is diluted,its $pH$ .....

Calculate the degree of hydrolysis of a salt formed from $0.1 \ N$ $NH_4OH$ and $0.1 \ N$ $HCN$. Given $K_a = 10^{-5}$ and $K_b = 10^{-5}$.

Find the equilibrium constant for the equilibrium reaction:
$HCOO^{-} + H_2O \rightleftharpoons HCOOH + OH^{-}$
Given that the dissociation constant of formic acid is $K_a(HCOOH) = 1.8 \times 10^{-4}$.

When solid potassium cyanide $(KCN)$ is added to water,then:

$A$ weak acid with $pK_a$ $5.9$ and a weak base with $pK_b$ $5.8$ are mixed in equal proportions. The $pH$ of the resulting solution is: