Answer : $X_8$
Mole fraction of solvent =$\large\frac{(100g/76gmol^{-1})}{(100g/76gmol^{-1})+(2g/M)}$
Hence $848.9$ Torr=$\large\frac{(100/76mol^{-1})}{(100/76mol^{-1})+(2g/M)}$(854 Torr)
Solving for M,we get $M=\large\frac{0.994\times 2g}{1.316(1-0.994)mol}$$=251.8gmol^{-1}$
Number of S atoms in a molecule of solute =$\large\frac{251.8amu}{32amu}$$=8$