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

Amongst the following solutions,the buffer solution is

The Henderson-Hasselbalch equation for an acidic buffer is given by $pH - pK_a = 5$. This condition holds true when:

All the given solutions have the same concentration. Mixing equal volumes of which of the following will produce a buffer solution?
$A = NH_4Cl$; $B = CH_3COONa$; $C = NH_4OH$; $D = CH_3COOH$

Components of a buffer solution are $0.1 \ M \ HCN$ and $0.2 \ M \ NaCN$. What is the $pH$ of the solution? (Given: $pK_a$ of $HCN = 9.30$)

The condition for minimum change in $pH$ for a buffer solution is