The equivalent weight of Ca in ${\mathrm{CaCO}}_3 \mathrm{is}$

Equivalent weight of $\mathrm{Ca}=\frac{\mathrm{Atomic} \mathrm{weight} \mathrm{of} \mathrm{Ca}}{\mathrm{Valency} \mathrm{of} \mathrm{Ca}}$

Calcium belongs to $2^{\mathrm{nd}} \mathrm{group}, \mathrm{so} \mathrm{its} \mathrm{valency} \mathrm{is} 2$

Therefore, equivalent weight of Ca $=\frac{40}{2}=20$