The sulphate of an element contains $42.2\%$ element. The equivalent mass would be

Let $X$ be the element then the formula would be : ${XSO}_4$

Since the element is $42.2\%$, the ${SO}_4$ would be :

$100\%-42.2\%=57.8\%$

Molar mass of ${SO}_4$ :

$64+32=96 g/\text{ mole }$

This represents $57.8\%$

Mass of element is thus: $\frac{0.422}{0.578} \times 96 = 70.09$

Equivalent weight = molecular weight/valency factor.

Therefore the equivalent weight $=70.09/2=35$  ( valency factor for sulphates is 2).

Hence option B is the correct answer.