In which of the following compounds, oxygen exhibits fractional oxidation state?

In the reaction ${\left({\mathrm{NH}}_4\right)}_2{\mathrm{Cr}}_2{\mathrm{O}}_7\to {\mathrm{N}}_2+4{\mathrm{H}}_2\mathrm{O}+{\mathrm{Cr}}_2{\mathrm{O}}_3$,

What is the number of electrons lost by each $\mathrm{N}$ atom?

In the half-reaction ${\mathrm{S}}_2{\mathrm{O}}_3^{-2}\rightleftharpoons {\mathrm{S}}_4{\mathrm{O}}_6^{-2}$, what is the number of electrons that must be added?

${\mathrm{Cu}}_2\mathrm{S}+{\mathrm{MnO}}_4^{-}\rightleftharpoons {\mathrm{Cu}}^{2+}+{\mathrm{SO}}_2+{\mathrm{Mn}}^{2+}$

How many electrons will be lost from $1$ mole of ${\mathrm{Cu}}_2\mathrm{S}$ in the above reaction?

${\mathrm{C}}_2{{\mathrm{O}}_4}^{2-}+{{\mathrm{MnO}}_4}^{-}\to {\mathrm{Mn}}^{2+}+{\mathrm{CO}}_2$

The above reaction takes place in

Which among the following are the cases of disproportionation reaction?

a. ${\mathrm{Cl}}_2+2{\mathrm{OH}}^{-}\to {\mathrm{Cl}}^{-}+{\mathrm{H}}_2\mathrm{O}+{\mathrm{ClO}}_3^{-}$

b. $2\mathrm{HgO}\to 2\mathrm{Hg}+{\mathrm{O}}_2$

c. $2{\mathrm{HCuCl}}_2\to \mathrm{Cu}+{\mathrm{Cu}}^{2+}+4{\mathrm{Cl}}^{-}+2{\mathrm{H}}^{+}$

d. ${\mathrm{MgCO}}_3\to \mathrm{MgO}+{\mathrm{CO}}_2$

$\mathrm{S}+12{\mathrm{OH}}^{-}\to 4{\mathrm{S}}^{2-}+2{\mathrm{S}}_2{\mathrm{O}}_3^{2-}+6{\mathrm{H}}_2\mathrm{O}$

The molecular state of sulphur as a reactant in the above reaction is