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

Which one of the following compounds does not decolourise an acidified aqueous solution of $KMnO_4$?

In acidic medium,the required number of moles of ferrous oxalate $(FeC_2O_4)$ for the reduction of $2.5 \, mol$ of $KMnO_4$ is:

In chloro-alkali industries,during the Solvay ammonia process,a redox change occurs during:

Assign $A, B, C, D$ from the given type of reaction.
$CrCl_3$ $(aq)$ + $ZnSO_4$ $(aq)$ $\longrightarrow$ No reaction

The unbalanced chemical reactions given in List-$I$ show missing reagent or condition $(?)$ which are provided in List-$II$. Match List-$I$ with List-$II$ and select the correct answer using the code given below the lists:

List-$I$	List-$II$
$P. \ PbO_2 + H_2SO_4 \xrightarrow{?} PbSO_4 + O_2 + \text{other product}$	$1. \ NO$
$Q. \ Na_2S_2O_3 + H_2O \xrightarrow{?} NaHSO_4 + \text{other product}$	$2. \ I_2$
$R. \ N_2H_4 \xrightarrow{?} N_2 + \text{other product}$	$3. \ \text{Warm}$
$S. \ XeF_2 \xrightarrow{?} Xe + \text{other product}$	$4. \ Cl_2$

Codes: $P \quad Q \quad R \quad S$