A \(5\%\) solution of cane sugar (molecular weight \(= 342\)) is isotonic with \(1\%\) solution of substance \(X\). The molecular weight of \(X\) is?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 68.4 g
Two solutions with the same osmotic pressure at the same temperature are isotonic. Since π = CRT, isotonic solutions of non-electrolytes have the same molar concentration.
5% cane sugar: 5 g in 100 mL → moles = 5/342
1% X: 1 g in 100 mL → moles = 1/M
Equal concentrations (same volume):
5/342 = 1/M
M = 342/5 = 68.4 g mol−1
NCERT (2026-27 edition):
Osmosis and Osmotic Pressure – …
