Which one of the following conversions does not involve either oxidation or reduction?

$PbO$ and $PbO_2$ react with $HCl$ according to the following chemical equations:
$(i)$ $2PbO + 4HCl \to 2PbCl_2 + 2H_2O$
$(ii)$ $PbO_2 + 4HCl \to PbCl_2 + Cl_2 + 2H_2O$
Why do these compounds differ in their reactivity?

Match List-$I$ with List-$II$.

List-$I$ (Types of redox reactions)	List-$II$ (Examples)
$a.$ Combination reaction	$(i)$ $Cl_{2(g)} + 2Br^-_{(aq)} \rightarrow 2Cl^-_{(aq)} + Br_{2(l)}$
$b.$ Decomposition reaction	$(ii)$ $2H_2O_{2(aq)} \rightarrow 2H_2O_{(l)} + O_{2(g)}$
$c.$ Displacement reaction	$(iii)$ $CH_{4(g)} + 2O_{2(g)} \xrightarrow{\Delta} CO_{2(g)} + 2H_2O_{(l)}$
$d.$ Disproportionation reaction	$(iv)$ $2H_2O_{(l)} \xrightarrow{\text{electrolysis}} 2H_{2(g)} + O_{2(g)}$

Choose the correct answer from the options given below.

What is the maximum number of moles of electrons taken up by one mole of $NO_3^-$ when it is reduced to the given products?

Whenever a reaction between an oxidising agent and a reducing agent is carried out,a compound of lower oxidation state is formed if the reducing agent is in excess and a compound of higher oxidation state is formed if the oxidising agent is in excess. Justify this statement giving three illustrations.

$500$ mL of $0.2$ $M$ $MnO_4^-$ solution in basic medium when mixed with $500$ mL of $1.5$ $M$ $KI$ solution, oxidises iodide ions to liberate molecular iodine. This liberated iodine is then titrated with a standard $x$ $M$ thiosulphate solution in presence of starch. If $300$ mL of thiosulphate was consumed, then the value of $x$ is . . . . . . .