$$2 \mathrm{Cl}^{-}(a q)+2 \mathrm{H}_2 \mathrm{O}(l) \longrightarrow 2 \mathrm{OH}^{-}(a q)+\mathrm{H}_2(g)+\mathrm{Cl}_2(g)$$

For the given reaction, value of $\Delta G^{\circ}$ is +422 kJ.

Using $\Delta G^{\circ}=-n F E^{\circ}$, the value of $E^{\circ}=-2.2 \mathrm{~V}$.

Therefore, an external emf greater than 2.2 V is required for the extraction of $\mathrm{Cl}_2$ from brine.

Using Ellingham diagram, we observe that at temperature greater than 1073 K ; $\Delta G_{(\mathrm{C}, \mathrm{CO})}<\Delta G_{(\mathrm{Fe}, \mathrm{FeO})}$. We know that according to Ellingham diagram, compound having lower $\Delta_f G^s$ undergo its formation. Hence, coke can reduce FeO to Fe .

(a) $\underset{\begin{array}{c}\text { Hematite } \\ \text { lining }\end{array}}{\mathrm{Fe}_2 \mathrm{O}_3}+\underset{\begin{array}{c}\text { Impurities } \\ \text { (present in cast iron) }\end{array}}{3 \mathrm{C}} \longrightarrow \underset{\substack{\text { Wrought } \\ \text { iron }}}{2 \mathrm{Fe}}+3 \mathrm{CO}$

This reaction takes place in reverberatory furnace lined with haematite.

(b) The haematite oxidises S to $\mathrm{SO}_2$, Si to $\mathrm{SiO}_2$ and P to $\mathrm{P}_4 \mathrm{O}_{10}$. Sometimes limestone is added as flux. Impurities of $\mathrm{S}, \mathrm{Si}$ and P oxidise and pass into slag. The metal is removed and freed from slag by passing through rollers.

Copper is extracted from low grade copper ore using hydrometallurgy method. For this purpose, ore is leached out using bacteria. The solution containing $\mathrm{Cu}^{2+}$ is treated with scrap iron and $\mathrm{H}_2$.

$$\mathrm{Cu}^{2+}(a q)+\mathrm{H}_2(g) \longrightarrow \mathrm{Cu}(s)+2 \mathrm{H}^{+}(a q)$$