An organic compound contains C, H and S. The minimum molecular weight of the compound containing 8% sulphur is: (atomic weight of S = 32)

8% sulphur implies that 8 g of sulphur is present in 100 g of the compound. The minimum molecular weight of the compound is obtained when 32 g of sulphur (i.e. one mole of sulphur) is present. Thus minimum molecules 

weight $=\left(\frac{100}{8}\right)\left(32\right)=400$