Based on the following information,arrange four metals $A, B, C$ and $D$ in order of decreasing ability to act as reducing agents:
$[I]$ Only $A, B$ and $C$ react with $1 \ M \ HCl$ to give $H_2 \ (g)$.
$[II]$ When $C$ is added to solutions of the other metal ions,metallic $B$ and $D$ are formed.
$[III]$ Metal $C$ does not reduce $A^{n+}$.

Consider the cell reaction at $300 \ K$: $A_{(s)} + B^{2+}_{(aq)} \rightleftharpoons A^{2+}_{(aq)} + B_{(s)}$. Its $E^{\circ}$ is $1.0 \ V$. The $\Delta_{r}H^{\circ}$ of the reaction is $-163 \ kJ \ mol^{-1}$. What is $\Delta_{r}S^{\circ}$ (in $J \ K^{-1} \ mol^{-1}$) of the reaction? $(F = 96500 \ C \ mol^{-1})$

Impure copper containing $Fe$,$Au$,and $Ag$ as impurities is electrolytically refined. $A$ current of $140 \ A$ for $482.5 \ s$ decreased the mass of the anode by $22.26 \ g$ and increased the mass of the cathode by $22.011 \ g$. The percentage of iron in the impure copper is (Given molar mass $Fe = 55.5 \ g \ mol^{-1}$,molar mass $Cu = 63.54 \ g \ mol^{-1}$)

Copper from copper sulphate solution can be displaced by .............. The standard reduction potentials of some electrodes are given below:
$E^o (Fe^{2+}, Fe) = -0.44 \ V$
$E^o (Zn^{2+}, Zn) = -0.76 \ V$
$E^o (Cu^{2+}, Cu) = +0.34 \ V$
$E^o (Cr^{2+}, Cr) = -0.74 \ V$
$E^o (H^{+}, 1/2H_2) = 0.00 \ V$

Consider the strong electrolytes $Z_{m}X_{n}$,$U_{m}Y_{p}$ and $V_{m}X_{n}$. Limiting molar conductivity $(\Lambda^0)$ of $U_{m}Y_{p}$ and $V_{m}X_{n}$ are $250 \ S \ cm^2 \ mol^{-1}$ and $440 \ S \ cm^2 \ mol^{-1}$,respectively. The value of $(m + n + p)$ is . . . . . Given:

$Ion$	$\lambda^0 \ (S \ cm^2 \ mol^{-1})$
$U^{p+}$	$50.0$
$Y^{m-}$	$50.0$
$V^{n+}$	$60.0$
$X^{m-}$	$50.0$
$Z^{n+}$	$40.0$

$\lambda^0$ is the limiting molar conductivity of ions. The plot of molar conductivity $(\Lambda)$ of $Z_{m}X_{n}$ $vs$ $c^{1/2}$ is given below.

The solubility product of $AgCl$ under standard conditions of temperature is given by