${\mathbf{S}}_1:$ The $\mathrm{pH}$ of solution made by dissolving $1 \mathrm{mole}$ each of $\mathrm{HCl},$ $\mathrm{NaOH}$  $\& {\mathrm{CH}}_3{\mathrm{COONH}}_4$ in the same beaker is $7,$ if ${\mathrm{pK}}_{\mathrm{a}}\left({\mathrm{CH}}_3\mathrm{COOH}\right)={\mathrm{pK}}_{\mathrm{b}}\left({\mathrm{NH}}_3\right)$.
${\mathbf{S}}_2:$ Methyl orange can be used as an indicator in the titration of ${\mathrm{CH}}_3\mathrm{COOH}$ with$\mathrm{NaOH}.$

 ${\mathrm{S}}_3$: Water act as an acid when ammonia is dissolved in water.