$100 \mathrm{mL}$ of $0.05 \mathrm{M} {\mathrm{C}}_3{\mathrm{N}}_2{\mathrm{H}}_{12}{\mathrm{SO}}_4$ (salt of Propane$-1,2-$diamine and ${\mathrm{H}}_2{\mathrm{SO}}_4$ ) and some volume of $0.1 \mathrm{M}$ ${\mathrm{C}}_3{\mathrm{N}}_2{\mathrm{H}}_{11}\mathrm{Cl}$ (salt of propane$-1,2-$diamine and $\mathrm{HCl}$) are available. What volume (in $\mathrm{mL}$) of $2^{\mathrm{nd}}$ salt solution should be taken to prepare a buffer solution of $\mathrm{pH}=6.31?$ Given: ${\mathrm{pK}}_{\mathrm{b}1} \& {\mathrm{pK}}_{\mathrm{b}2}$ of propane$-1, 2-$diamine are $4.18 \text{and} 7.39$ respectively.

Select the correct set of statements for an acid type indicator used in a titration:
$\left(\mathrm{i}\right)$ In general, $\mathrm{pH}$ range of an indicator is $\left({\mathrm{pK}}_{\mathrm{a}}-1\right)$ to $\left({\mathrm{pK}}_{\mathrm{a}}+1\right)$ and indicator shows its characteristic colours in this range.

$\left(\mathrm{ii}\right)$ In general, $\mathrm{pH}$ range of an indicator is $\left({\mathrm{pK}}_{\mathrm{a}}-1\right)$ to $\left({\mathrm{pK}}_{\mathrm{a}}+1\right)$ and indicator does not show its characteristic colours in this range.

$\left(\mathrm{iii}\right)$ In the relation : $\mathrm{pH}={\mathrm{pK}}_{\mathrm{In}}+{\log }_{10}\frac{\left[{\ln }^{-}\right]}{\left[\mathrm{Hln}\right]}, \mathrm{pH}$ value represents $\mathrm{pH}$ of indicator solution.

$\left(\mathrm{iv}\right)$ In the relation : $\mathrm{pH}={\mathrm{pK}}_{\mathrm{In}}+{\log }_{10}\frac{\left[{\ln }^{-}\right]}{\left[\mathrm{Hln}\right]}, \mathrm{pH}$ value represents $\mathrm{pH}$ of resulting solution containing indicator.