Which ion undergoes disproportionation in an aqueous solution?

When $Cl_2$ gas reacts with hot and concentrated sodium hydroxide solution,the oxidation number of chlorine changes from

The disproportionation of $MnO_{4}^{2-}$ in acidic medium results in the formation of two manganese compounds $A$ and $B$. If the oxidation state of $Mn$ in $B$ is smaller than that of $A$,then the spin-only magnetic moment $(\mu)$ value of $B$ in $BM$ is $.........$ (Nearest integer).

Assign $A$,$B$,$C$,$D$ from given type of reaction.
$A$ for precipitate formation reaction.
$B$ for precipitate dissolution reaction.
$C$ for precipitate exchange reaction.
$D$ for no reaction.
$P_4 + 3NaOH + 3H_2O \longrightarrow PH_3 + 3NaH_2PO_2$
Identify the correct category for the given reaction.

Refer to the periodic table and answer the following questions:
$(a)$ Select the possible non-metals that can show disproportionation reaction.
$(b)$ Select three metals that can show disproportionation reaction.

$1 \text{ mole}$ of $MnO_4^{2-}$ disproportionates into $MnO_4^-$ and $MnO_2$ in an acidic medium. Calculate the percentage by mass of $Mn$ converted to $MnO_4^-$ (Molar mass of $Mn = 55 \ g/mol$).