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 $A^{n+}$.

The values of the limiting molar conductivity $(\lambda^0)$ for $NaCl$,$HCl$ and $NaOAc$ are $126.4$,$425.9$ and $91.0 \, S \, cm^2 \, mol^{-1}$,respectively. For $HOAc$,$\Lambda^0$ in $S \, cm^2 \, mol^{-1}$ is

Consider the following statements pertaining to fuel cells :-
$(a)$ Hydrogen-oxygen fuel cells make use of concentrated $KOH$ solution as an electrolyte and porous graphite impregnated with platinum as electrodes.
$(b)$ The efficiency of a fuel cell is less than unity due to polarization at electrodes and the resistance offered by the electrode and the electrolyte.
$(c)$ The electrical work,assuming the cell to be working reversibly,may be represented as $-\Delta G = W_{\text{electrical}} = -\Delta H + T\Delta S$.
Which of the above statements are correct?

During the electrolysis of concentrated $H_2SO_4$,perdisulphuric acid $(H_2S_2O_8)$ and $O_2$ are formed at the anode in equimolar amounts. The moles of $H_2$ that will form simultaneously at the other electrode will be (Given: $2H_2SO_4 \rightarrow H_2S_2O_8 + 2H^+ + 2e^-$)

For a saturated solution of $Ag_{2}CrO_{4}$ at infinite dilution,$\lambda_{m}^{\infty}(Ag^{+}) = 127 \ \Omega^{-1} \ cm^{2} \ mol^{-1}$ and $\lambda_{m}^{\infty}(CrO_{4}^{2-}) = 246 \ \Omega^{-1} \ cm^{2} \ mol^{-1}$. If the specific conductance of the solution is $2 \times 10^{-2} \ \Omega^{-1} \ cm^{-1}$,calculate the solubility product $(K_{sp})$ of $Ag_{2}CrO_{4}$.

During electrolysis of aqueous $NaOH$,$4 \ g$ of $O_2$ gas is liberated at $NTP$ at the anode. The volume of $H_2$ gas liberated at the cathode in $litres$ is $..............$