Mol.wt of chloride $MCl_n=59.25\times 2=118.50$

Suppose atomic mass of M=a

$a+35.5n=118.5$

Eq.mass=$\large\frac{\text{At.mass}}{\text{Valency}}$

At.mas=$E\times n$

Where $n$=valency (or) $E\times n+35.5n=118.5$

Where $E=4$(given)

$4n+35.5n=118.5$

$n=3$

Hence (b) is the correct answer.