Correct answer is : 4
\(\mathrm{MnO}_2+\mathrm{KOH}+\mathrm{O}_2 \rightarrow \underset{(A)}{K_2MnO_4} +H_2O\)
\(\mathrm{K}_2 \mathrm{MnO}_4 \xrightarrow{\text { Neutral/acidic solution }} \mathrm{KMnO}_4+\mathrm{MnO}_2\)
\(\mathrm{Mn}^{+4}:-[\mathrm{Ar}] 3 \mathrm{~d}^3\)
\(\mathrm{n}=3, \mu=\sqrt{3(3+2)}=3.87 \text { B.M. }\)
Nearest integer is (4)