By passing $H_2S$ gas in acidified $KMnO_4$ solution,we get

Why do the following reactions proceed differently? $Pb_{3}O_{4} + 8HCl \rightarrow 3PbCl_{2} + Cl_{2} + 4H_{2}O$ and $Pb_{3}O_{4} + 4HNO_{3} \rightarrow 2Pb(NO_{3})_{2} + PbO_{2} + 2H_{2}O$

What volume of $O_{2(g)}$ measured at $1 \ atm$ and $273 \ K$ will be formed by the action of $100 \ mL$ of $0.5 \ N \ KMnO_4$ on hydrogen peroxide in an acidic solution? The skeleton equation for the reaction is: $KMnO_4 + H_2SO_4 + H_2O_2 \to K_2SO_4 + MnSO_4 + O_2 + H_2O$.

Given below are two statements:
Statement-$I$ : Heating $NaCl$ with concentrated $H_2SO_4$ and $MnO_2$ results in oxidation of $Mn$.
Statement-$II$ : Heating $NaI$ with concentrated $H_2SO_4$ and $MnO_2$ results in reduction of $Mn$.
In light of the above statements, choose the most appropriate answer from the options given below:

Which of the following act as an oxidising as well as a reducing agent?

When an acidic solution of $K_2Cr_2O_7$ is added to $Na_2SO_3$,it turns green. Which of the following compounds is formed in this reaction?