Which of the following does not show a disproportionation reaction?

Which of the following chemical substances undergoes self-oxidation and self-reduction during the same reaction?

Which of the following reactions are disproportionation reactions?
$(a)$ $2 Cu^{+} \rightarrow Cu^{2+} + Cu^{0}$
$(b)$ $3 MnO_{4}^{2-} + 4 H^{+} \rightarrow 2 MnO_{4}^{-} + MnO_{2} + 2 H_{2}O$
$(c)$ $2 KMnO_{4} \xrightarrow{\Delta} K_{2}MnO_{4} + MnO_{2} + O_{2}$
$(d)$ $2 MnO_{4}^{-} + 3 Mn^{2+} + 2 H_{2}O \rightarrow 5 MnO_{2} + 4 H^{+}$
Select the correct option from the following:

What is obtained when $H_2S$ gas is passed through $Hg_2^{2+}$ solution?

Which of the following substances acts as both an oxidizing agent and a reducing agent?

Nitrous acid was disproportionated to form water,$HNO_3$ and $X$. In another reaction,sodium nitrite was reacted with $H_2SO_4$ to form $NaHSO_4, HNO_3$,water and $Y$. What are $X$ and $Y$ respectively?