Class $\mathrm{XII}$ students were asked to prepare one litre of buffer solution of $\mathrm{pH} 8.26$ by their chemistry teacher. The amount of ammonium chloride to be dissolved by the student in $0.2\mathrm{M}$ ammonia solution to make one litre of the buffer is (Given ${\mathrm{pK}}_{\mathrm{b}}\left({\mathrm{NH}}_3\right)=4.74;$ Molar mass of ${\mathrm{NH}}_3=17 \mathrm{g}{ \mathrm{mol}}^{-1}$. Molar mass of ${\mathrm{NH}}_4\mathrm{Cl}=53.5 \mathrm{g}{ \mathrm{mol}}^{-1}$)

Given below are two statements: one is labelled as Assertion $\mathrm{A}$ and the other is labelled as Reason $\mathrm{R}$.

Assertion $\mathrm{A}$ :Phenolphthalein is a $\mathrm{pH}$ dependent indicator, remains colourless in acidic solution and gives pink colour in basic medium

Reason $\mathrm{R}$ : Phenolphthalein is a weak acid. It doesn't dissociate in basic medium.

In the light of the above statements, choose the most appropriate answer from the options given below

At $600 \mathrm{K},2 \mathrm{mol}$ of $\mathrm{NO}$ are mixed with $1 \mathrm{mol}$ of ${\mathrm{O}}_2$.

$2{\mathrm{NO}}_{\left(\mathrm{g}\right)}+{\mathrm{O}}_2\left(\mathrm{g}\right)\rightleftarrows 2{\mathrm{NO}}_2\left(\mathrm{g}\right)$

The reaction occurring as above comes to equilibrium under a total pressure of $1$ atm. Analysis of the system shows that $0.6 \mathrm{mol}$ of oxygen are present at equilibrium. The equilibrium constant ${\mathrm{K}}_{\mathrm{p}}$ for the reaction is____. Give an answer to the nearest integer value.