On treating $SO_2$ with an aqueous solution of $KMnO_4$,the manganese ion reduces to

Acidified potassium permanganate solution is decolourised by

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$SrCrO_4 \downarrow + 2AcOH \text{ (Excess)} \longrightarrow Sr(AcO)_2 + H_2Cr_2O_7$

In the following reaction,identify the oxidation states of the underlined phosphorus atoms in the products formed by complete hydrolysis at $R.T.$:
$H_4\underline{P}_2O_6 + H_2O \longrightarrow H_3PO_3 + H_3PO_4$

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

In which of the following reactions does the oxidation number not change?