$A$ certain buffer solution contains equal concentrations of $3.9 \times 10^{-5} \ M$ $X^{-}$ and $HX$. The $K_b$ for $X^{-}$ is $10^{-10}$. The $pH$ of the buffer is:

Find the concentration of sodium acetate when added to $0.1 \ M$ solution of acetic acid to form a buffer solution of $pH = 5.5$ (in $M$)? $(pK_{a} \text{ of } CH_{3}COOH = 4.5)$

What is the $OH^-$ ion concentration of a solution containing $0.05 \, M$ ammonium hydroxide and $0.001 \, M$ ammonium chloride? Given $K_b(NH_4OH) = 1.8 \times 10^{-5}$.

The $pH$ of an acidic buffer mixture is

Assertion $(A)$: The $pH$ of a buffer solution containing equal moles of acetic acid and sodium acetate is $4.8$ ($pK_a$ of acetic acid is $4.8$).
Reason $(R)$: The ionic product of water at $25^{\circ} C$ is $10^{-14} \ mol^2 \ L^{-2}$. The correct answer is

Find the value of $\frac{[NaCN]}{[HCN]}$ given the $pH$ of the buffer solution of $NaCN$ and $HCN$ is $9.3$ and $K_a$ of $HCN$ is $5 \times 10^{-10}$.