Which of the following can act as both an oxidizing and a reducing agent?

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

Assign $A, B, C, D$ from the given type of reaction.
$Hg_2(NO_3)_2 + 2NH_3(aq) + H_2O \longrightarrow Hg \downarrow + Hg(NH_2)NO_3 \downarrow + NH_4NO_3$
(Note: The reaction represents the disproportionation of mercury$(I)$ nitrate with ammonia.)

Which of the following best describes the behavior of bromine in the reaction given below?
$H_2O + Br_2 \to HOBr + HBr$

Which is the best description of the behaviour of bromine in the reaction given below $H_2O + Br_2 \to HOBr + HBr$?

The products $P$ and $Q$ of the following reaction,respectively,are $a S_{8(s)} + b NaOH_{(aq)} \longrightarrow P_{(aq)} + q Q_{(aq)} + r H_2O$