The $pK_a$ of an equimolar mixture of sodium acetate and acetic acid is $4.74$. What is the $pH$ of the solution?

Which one of the following pairs of solutions is not an acidic buffer?

$A$ buffer solution contains $1 \ mol$ of ammonium sulphate and $1 \ mol$ of $NH_4OH$ $(K_b = 10^{-5})$. The $pH$ of the solution will be:

The $pKa$ of a weak acid $HA$ is $4.5$. The $pOH$ of an aqueous buffer solution in which the acid $HA$ is $50\%$ ionized is:

$A$ solution is prepared by mixing $0.01 \ mol$ each of $H_2CO_3$,$NaHCO_3$,$Na_2CO_3$,and $NaOH$ in $100 \ mL$ of water. The $pH$ of the resulting solution is. . . . . . .
[Given : $pK_{a1}$ and $pK_{a2}$ of $H_2CO_3$ are $6.37$ and $10.32$,respectively; $\log 2=0.30$ ]

What is $[H^{+}]$ in $mol/L$ of a solution that is $0.20\, M$ in $CH_3COONa$ and $0.10\, M$ in $CH_3COOH$? $K_a$ for $CH_3COOH = 1.8 \times 10^{-5}$.