$W \ g$ of a non-volatile electrolyte solid solute of molar mass $M \ g \ mol^{-1}$ when dissolved in $100 \ mL$ water, decreases vapor pressure of water from $640 \ mm \ Hg$ to $600 \ mm \ Hg$. If aqueous solution of the electrolyte boils at $375 \ K$ and $K_b$ for water is $0.52 \ K \ kg \ mol^{-1}$, then the mole fraction of the electrolyte solute $(X_2)$ in the solution can be expressed as (Given density of water $= 1 \ g/mL$ and boiling point of water $= 373 \ K$):

• A
  $\frac{1.3}{8} \times \frac{W}{M}$
• B
  $\frac{16}{2.6} \times \frac{W}{M}$
• C
  $\frac{2.6}{16} \times \frac{M}{W}$
• D
  $\frac{1.3}{8} \times \frac{M}{W}$