The molecular formula of a commercial resin used for exchanging ions in water softening is $C_8H_7SO_3Na$ (Mol.wt.206) What would be the maximum uptake of $Ca^{2+}$ ions by the resin when expressed in mole per gram resin ?

Question

$\begin{array}{1 1} \frac{1}{412} \\ \frac{1}{103} \\ \frac{1}{206} \\ \frac{2}{309} \end{array}$