The $$\mathrm{E}^{\circ}$$ values of $$\mathrm{A} . \mathrm{B}$$ and $$\mathrm{C}$$ are given. Which element/(s) is/(are) good for coating the surface of iron to prevent corrosion? Given: $$[\mathrm{E}_{\mathrm{Fe}^{2+} / \mathrm{Fe}}^0=-0.44 \mathrm{~V} ; \quad \mathrm{E}_{\mathrm{A}^{2+} / \mathrm{A}}^0=-2.37 \mathrm{~V} ; \quad \mathrm{E}_{\mathrm{B}^{2+} / \mathrm{B}}^0=-0.15 \mathrm{~V} ; \quad \mathrm{E}_{\mathrm{C}^{2+} / \mathrm{C}}^0=+0.34 \mathrm{~V}]$$

The limiting molar conductivity of $$\mathrm{NH}_4 \mathrm{OH}$$ is $$238 \mathrm{~S} \mathrm{~cm}^2 \mathrm{~mol}^{-1}$$. At $$25^{\circ} \mathrm{C}$$, molar conductance of $$0.1 \mathrm{M}$$ aqueous solution of ammonium hydroxide is $$9.54 \mathrm{~S} \mathrm{~cm}^2 \mathrm{~mol}^{-1}$$. The degree of ionisation of $$\mathrm{NH}_4 \mathrm{OH}$$ at the same concentration and temperature is:

What would be the EMF of the cell in which the following reaction occurs:

$$\begin{aligned} & \mathrm{Cd}(\mathrm{S})+2 \mathrm{H}^{+} \rightarrow \mathrm{Cd}^{2+}+\mathrm{H}_{2(\mathrm{~g})} \\ & {\left[\mathrm{H}^{+}\right]=0.02 \mathrm{M} \quad \mathrm{E}^0\left(\mathrm{Cd}^{2+} / \mathrm{Cd}\right)=-0.4 \mathrm{~V},\left[\mathrm{Cd}^{2+}\right]=0.01 \mathrm{M} \text { and partial pressure of } \mathrm{H}_2 \text { gas }=0.8 \mathrm{~atm} .} \end{aligned}$$

Propane in presence of $$\mathrm{O}_2$$ gas undergoes complete combustion to produce $$\mathrm{CO}_2$$ and $$\mathrm{H}_2 \mathrm{O}$$. The required $$\mathrm{O}_2$$ for this combustion reaction was produced by the electrolysis of water. For what duration of time had water been electrolysed by passing $$200 \mathrm{~A}$$ current so that Oxygen gas produced could completely burn $$44 \mathrm{~g}$$ of Propane?