The number of Faradays (F) required to produce 20 g of calcium from molten CaCl₂ (Atomic mass of Ca=40 g mol^-1 ) is

According to Faraday’s 1^st law, $\mathrm{m\alpha Q}$
m = EQ
where, 
m = mass of a substance deposited
Q = current in Faraday’s
Given m = 20 g,
E = Equivalent weight of $\mathrm{Ca}=\frac{\mathrm{40}}{\mathrm{2}}=20$
$\mathrm{Q}=\frac{\mathrm{m}}{\mathrm{E}}\mathrm{=}\frac{\mathrm{20}}{\mathrm{20}}=1\mathrm{F}$