Auto-oxidation of bleaching powder gives

An example of a disproportionation reaction is

When white phosphorus reacts with caustic soda $(NaOH)$,$PH_3$ and $NaH_2PO_2$ are formed. This reaction is an example of what?

Which of the following processes is not associated with steel making?

Among $P_4$,$S_8$ and $N_2$,the elements which undergo disproportionation when heated with $NaOH$ solution are:

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.