${\mathrm{H}}_3{\mathrm{PO}}_4$ undergoes dissociation as ${\mathrm{H}}_3{\mathrm{PO}}_4⟶3{\mathrm{H}}^{+}+{\mathrm{PO}}_4^{3-}$ if $\frac{{\mathrm{n}}_{\text{cation }}+{\mathrm{n}}_{\text{anion }}}{{\left({\mathrm{n}}_{{\mathrm{H}}_3{\mathrm{PO}}_4}\right)}_{\text{undissoicated }}}=\frac{8}{3}$. $\%$ dissociation of ${\mathrm{H}}_3{\mathrm{PO}}_4$ is " $\mathrm{x}$ ", report your answer as $\left[\frac{\mathrm{x}}{10}\right]$

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

The degree of dissociation of $0.1\mathrm{mol} {\mathrm{L}}^{-1}$acetic acid in water is

( $\mathrm{K}$ of acetic acid is ${10}^{-5}$ ) 

$0.01$ moles of a weak acid $\mathrm{HA} \left({\mathrm{K}}_{\mathrm{a}}=2.0\times {10}^{-6}\right)$ is dissolved in $1.0 \mathrm{L}$ of $0.1\mathrm{M} \mathrm{HCl}$ solution. The degree of dissociation of $\mathrm{HA}$ is __________ $\times {10}^{-5}$ (Round off to the Nearest Integer). [Neglect volume change on adding $\mathrm{HA}$ and assume degree of dissociation $<<1$]