When ${\mathrm{Cl}}_2$ water is dropwise added into $\mathrm{KI}$ solution, initially brown colouration appears, further on adding excess ${\mathrm{Cl}}_2$ water brown colouration disappears due to formation of colourless compound $\left(\mathrm{X}\right)$ predict oxidation state of central atom in compound $\left(\mathrm{X}\right)$.

How many of the following reactions (not balanced eqn) undergo disproportionation reaction?

i) $\underset{\mathrm{Cold} \& \mathrm{dil}}{\mathrm{NaOH}}+{\mathrm{Cl}}_2⟶$

ii) $\underset{\mathrm{Cold} \& \mathrm{dil}}{\mathrm{NaOH}}+{\mathrm{F}}_2⟶$

iii) $\mathrm{NaOH}+{\mathrm{P}}_4⟶$

iv) ${\mathrm{H}}_3{\mathrm{PO}}_3\stackrel{\mathrm{\Delta }}{⟶}$

v) ${\mathrm{NO}}_2\underset{{\mathrm{H}}_2\mathrm{O}}{\overset{\mathrm{Hot}}{\to }}$

vi) $\mathrm{NaOH}+{\mathrm{ClO}}_2⟶$

vii) ${\mathrm{HClO}}_2\underset{\mathrm{Oxidation}}{\overset{\mathrm{Auto}}{\to }}$

viii) ${\mathrm{HNO}}_2\underset{\mathrm{oxidation}}{\overset{\mathrm{Auto}}{\to }}$

Compound $2$ and $1$ are mixed in $1: 4$ molar ratio. The mixture was subjected to ammonium molybdite test for phosphate estimation. The results of the test yielded a phosphate concentration of $36\mathrm{mM}$ for the mixture. What is the concentration of compound $2$ in $\mathrm{mM}$ in the mixture?

${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_3, {\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_4, {\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_5, {\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_6, {\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_7, {\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_8, {\mathrm{H}}_2{\mathrm{SO}}_5$