What is $[H^{+}]$ of a solution that is $0.01 \ M$ in $HCN$ and $0.02 \ M$ in $NaCN$ ($K_a$ for $HCN = 6.2 \times 10^{-10}$)?

$A$ solution contains $0.1 \ mol$ of acetic acid and $0.1 \ mol$ of sodium acetate in $500 \ mL$ of solution. If the $pH$ of the solution is $4.74$,find the ionization constant $(K_a)$ of acetic acid.

$A$ solution is prepared by mixing $10 \ mL$ of $1.0 \ M$ acetic acid and $20 \ mL$ of $0.5 \ M$ sodium acetate and diluted to $100 \ mL$. If the $pK_{a}$ of acetic acid is $4.76$,then the $pH$ of the solution is

Give the importance of buffer solution.

What is the $pH$ of a solution prepared by mixing $20 \ mL$ of $0.250 \ M$ sodium formate with $30 \ mL$ of $0.100 \ M$ $HCl$ ($pK_a$ for $HCOOH = 3.75$):-

Which of the following is a buffer solution of strong acidic nature?