Question

A black compound ‘A’ in its solid state is fused with $KOH$ and $KCl{O}_3$. The aqueous extract of the fused mass is a green coloured solution ‘B’. On passing $C{O}_2$ gas through it, pink colour of ‘C’ is noticed along with some black insoluble mass of ‘A’. The pink coloured solution is decolourised by $F{e}^{2+}$ in acidic medium. The oxidation state of the central metal in ‘C’ is?

• A. $+4$
• B. $+5$
• C. $+6$
• D. $+7$

Answer 1

The correct option is D $+7$

$\underset{A\left(\text{black}\right)}{Mn{O}_2}+KOH+KCl{O}_3\stackrel{\Delta }{\to }\underset{B\left(\text{green}\right)}{K_{2}Mn{O}_4}+KCl+H_{2}O$

$\underset{B\left(\text{green}\right)}{K_{2}Mn{O}_4}+C{O}_2\to \underset{C\left(\text{pink}\right)}{KMn{O}_4}+\underset{A\left(\text{black}\right)}{Mn{O}_2}+K_{2}C{O}_3$

$\underset{C\left(\text{pink}\right)}{K\stackrel{+7}{Mn}{O}_4}+F{e}^{2+}\stackrel{H^{+}}{\to }\underset{\left(\text{colourless}\right)}{F{e}^{3+}+M{n}^{2+}}+H_{2}O$