The dissociation constant of $HCN$ is $5 \times 10^{-10}$. The $pH$ of the solution prepared by mixing $1.5 \, mole$ of $HCN$ and $0.15 \, mole$ of $KCN$ in water and making up the total volume to $0.5 \, dm^3$ is (in $.302$)

Assertion : Mixture of $CH_3COOH$ and $CH_3COONH_4$ is an example of acidic buffer.
Reason : Acidic buffer contains equimolar mixture of a weak acid and its salt with weak base.

$pH$ of $0.1 \ M$ solution of a weak acid $(HA)$ is $4.50$. It is neutralized with $NaOH$ solution to decrease the acid content to half. The $pH$ of the resulting solution is:

Which of the following is not a buffer solution?

Class $XII$ students were asked to prepare one litre of buffer solution of $pH$ $8.26$ by their chemistry teacher. The amount of ammonium chloride to be dissolved by the student in $0.2 \, M$ ammonia solution to make one litre of the buffer is $..... \, g$ (Given $pK_b(NH_3)=4.74$; Molar mass of $NH_3=17 \, g \, mol^{-1}$; Molar mass of $NH_4Cl =53.5 \, g \, mol^{-1}$)

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