$\mathrm{C}{\mathrm{r}}^{2+}$ and $\mathrm{M}{\mathrm{n}}^{3+}$ both have ${\mathrm{d}}^4$ configuration. Thus

A$0.5-\mathrm{g}$ sample containing ${\mathrm{MnO}}_2$ is treated with $\mathrm{HCl}$, liberating ${\mathrm{Cl}}_2$. The ${\mathrm{Cl}}_2$ is passed into a solution of $\mathrm{KI}$ and $30.0 {\mathrm{cm}}^3$ of $0.1 \mathrm{M} {\mathrm{Na}}_2{\mathrm{S}}_2{\mathrm{O}}_3$ is required to titrate the liberated iodine. Calculate the percentage of ${\mathrm{MnO}}_2$ in the sample.

[Answer has to be given up to one place of decimal]

Out of the $5$ different products formed in the following reaction, how many contains $\mathrm{O}$-atom(s)?

${\mathrm{KMnO}}_4 + {\mathrm{Na}}_2{\mathrm{O}}_{2 }+ {\mathrm{H}}_2{\mathrm{SO}}_4⟶$

The central metal ion is${\mathrm{sp}}^3{\mathrm{d}}^2$ hybridised in Brown ring complex $\left[\mathrm{Fe}{\left({\mathrm{H}}_2\mathrm{O}\right)}_5\mathrm{NO}\right]{\mathrm{SO}}_4$.The magnetic moment (spin only) of the complex is $\sqrt{\mathrm{x}}$ BM. Find the value of $\mathrm{x}$.