A compound contains $20\%$ sulphur. The molecular weight of the compound could be

Acc. to question,

20g of sulphur is present in 100g

then, 32g of sulphur is present in 160g

Now, most of the oxides with sulphur gives the ratio of 1:3(ratio of molecules)

So, if mass of sulphur is 160g mass of oxygen is 160x3=480g

Therefore, mass of the compound 160+480g=640g.

Hence option D is the correct answer.