The $pH$ of a buffer solution formed by mixing $30 \text{ mL}$ of $0.1 \text{ M } NH_4OH$ and $30 \text{ mL}$ of $1 \text{ M } NH_4Cl$ solutions is $8.6$. The $pK_b$ of $NH_4OH$ is

$pH$ of a mixture of $1 \ M$ benzoic acid $(pK_a = 4.20)$ and $1 \ M$ $C_6H_5COONa$ is $4.5$. What is the volume of benzoic acid required to prepare a $300 \ mL$ buffer solution (in $mL$)? $[\log 2 = 0.3]$

Which mixture forms a buffer when dissolved in $1 \, L$ of water?

What is the value of $[H^{+}]$ when $0.1 \ mol$ of $CH_3NH_2$ is mixed with $0.08 \ mol$ of $HCl$? Given $K_b = 5 \times 10^{-4}$.

Find the $pH$ when $0.2 \, mol$ of $HCl$ is added to $1 \, L$ of a solution containing $1 \, M$ $CH_3COOH$ and $1 \, M$ $CH_3COO^-$. Assume the total volume remains $1 \, L$. Given $K_a$ for $CH_3COOH = 1.8 \times 10^{-5}$.

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