NEET 2020 Chemistry Question 106 Solution

In molten calcium chloride ($$\text{CaCl}_2$$), calcium exists as divalent cations ($$\text{Ca}^{2+}$$). At the cathode, each calcium ion requires two electrons to deposit as metallic calcium: $$\text{Ca}^{2+} + 2e^- \to \text{Ca (s)}$$

By Faraday's second law of electrolysis, deposition of 1 mole of an element requires $$n$$ moles of electrons, where $$n$$ is the valency of the ion. Since 1 mole of electrons carries a charge of 1 Faraday ($$1\text{ F} = 96500\text{ C}$$): $$1\text{ mol of Ca (40 g)} \iff 2\text{ moles of electrons} = 2\text{ F}$$

$$\text{Moles of Ca} = \frac{\text{Given Mass}}{\text{Molar Mass}} = \frac{20\text{ g}}{40\text{ g mol}^{-1}} = 0.5\text{ mol}$$

$$\text{Number of Faradays} = \text{Moles} \times n = 0.5 \times 2 = 1\text{ F}$$ Thus, exactly 1 Faraday of charge is required.