The buffering action of a mixture of $CH_3COOH$ and $CH_3COONa$ is maximum when the ratio of salt to acid is equal to .......?

$pH$ of a mixture of $1 \ M \ HA$ $(pK_a = 4.2)$ and $1 \ M \ NaA$ is $4.5$. In $300 \ mL$ of buffer,the volume of $HA$ is $....... \ mL$ $[\log \ 2 = 0.3]$

$A$ 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

At $25 \, ^\circ C$,the $K_a$ for $HCN$ is $5 \times 10^{-10}$. What volume (in $mL$) of $5 \, M \, KCN$ solution must be added to $10 \, mL$ of $2 \, M \, HCN$ solution to maintain a constant $pH$ of $9$?

Which of the following mixtures of solutions can function as a buffer solution?

When $0.02 \ mol$ of $NaOH$ is added to $1 \ L$ of a buffer solution,its $pH$ changes from $5.75$ to $5.80$. What is the buffer capacity of the solution?