Answer:
Option B
Explanation:
$M$ = Mother
$S$ = Son
I) $M+S=50--------(1)$
II) $3(M+S)=5M-----(2)$
From II we get $2M-3S$ $\Leftrightarrow \frac{M}{S}$ $=\frac{3}{2}$
Thus, (II) alone gives the answer, but (I) alone doesn't give the answer.
$\therefore $ Correct answer is (B).