A non-electrolyte X ( $15 g L^{- 1}$ ) is isotonic at the same temperature with a solution containing $5.85 g L^{- 1}$ $NaCl$ (molar mass $58.5$ , complete dissociation) and $9.0 g L^{- 1}$ glucose (molar mass $180 g mo l^{- 1}$ ). The molar mass of X (in $g mo l^{- 1}$ ) is

Answer: D

Particle concentration of the reference solution

= 2 \times (5.85/58.5) + 9.0/180 = 0.20 + 0.05 = 0.25 mol L^{- 1}

. X must have the same concentration:

15/ M = 0.25

, so

M = 60 g mo l^{- 1}