To solve this problem, we need to determine the number of Faradays required to produce 20 g of calcium from molten $\mathrm{CaCl}_2. \\$First, we need to understand the electrochemical reaction involved:$\\$• The reduction of calcium ions to calcium metal is represented by the half-reaction:$\\ \mathrm{Ca}^{2+} + 2e^- \rightarrow \mathrm{Ca} \\$This reaction shows that 2 moles of electrons (2 Faradays) are required to produce 1 mole of calcium.$\\$Next, we calculate the number of moles of calcium in 20 g:$\\$• The atomic mass of calcium is given as 40 g/mol.$\\$• Therefore, the number of moles of calcium is:$\\$Number of moles of $\mathrm{Ca} = \frac{20 \ g}{40 \ g/mol} = 0.5 \,$mol$\\$Since 2 Faradays are required to produce 1 mole of calcium, the number of Faradays required to produce 0.5 moles is:$\\$Number of Faradays$= 0.5 \,$mol$\times 2 \,$F/mol$= 1 \,$F$\\$Thus, the number of Faradays required to produce 20 g of calcium is 1. This corresponds to Option 4.