Which of the following is $NOT$ a redox reaction?

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$Na_2CO_3 + Pb(NO_3)_2 \longrightarrow PbCO_3 \downarrow + 2NaNO_3$

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

The treatment of an aqueous solution of $3.74 \ g$ of $Cu(NO_3)_2$ with excess $KI$ results in a brown solution along with the formation of a precipitate. Passing $H_2S$ through this brown solution gives another precipitate $X$. The amount of $X$ (in $g$) is. . . . . [Given : Atomic mass of $H=1, N=14, O=16, S=32, K=39, Cu=63, I=127$ ]

In basic medium,$CrO_{4}^{2-}$ oxidises $S_{2}O_{3}^{2-}$ to form $SO_{4}^{2-}$ and itself changes into $Cr(OH)_{4}^{-}$. The volume of $0.154 \ M \ CrO_{4}^{2-}$ required to react with $40 \ mL$ of $0.25 \ M \ S_{2}O_{3}^{2-}$ is ........... $mL$ (Rounded-off to the nearest integer).

When silver nitrate is heated to red hot,what is formed?