Which among the following species acts as a self-indicator?

Which compound is formed when $H_2S$ gas is passed through an acidic solution of $KMnO_4$?

Assign $A, B, C, D$ from the given type of reaction for the following chemical equation:
$PCl_5 \xrightarrow{\Delta} PCl_3 + Cl_2$

The number of moles of $KMnO_4$ reduced by one mole of $KI$ in alkaline medium is:

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$2NaBr + MnO_2 + 2H_2SO_4 \longrightarrow MnSO_4 + Na_2SO_4 + Br_2 + 2H_2O$

Only $2 \ mL$ of $KMnO_4$ solution of unknown molarity is required to reach the end point of a titration of $20 \ mL$ of oxalic acid $(2 \ M)$ in acidic medium. The molarity of $KMnO_4$ solution is: (in $M$)