A factory produces 40 kg of calcium in two hours by electrolysis. How much aluminium can be produced by same current in 2 hours if current efficiency is 50%?

Number of equivalents of Ca produced = $\frac{\mathrm{mass}}{\mathrm{Eq}.\mathrm{wt}}=\frac{40\times 10-3}{20}=2\times {10}^{-3}$

mass of Al produced =$\frac{\% \mathrm{current} \mathrm{efficiency} }{100}\times \mathrm{number} \mathrm{of} \mathrm{equivalents}\times \mathrm{Eq}.\mathrm{wt}$

$=\frac{50}{100}\times 2\times 9=9 \mathrm{kg}$