At a certain temperature the values of the slope of the plot of osmotic pressure (π) against concentration (C in mol \(L^{-1}\)) of a certain polymer solution is 291 R. The temperature at which osmotic pressure measured is -
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 18°C
For a dilute solution the osmotic pressure is proportional to the molar concentration:
\( \displaystyle \pi = CRT \)
A plot of π against C is therefore a straight line through the origin with slope = RT.
\( \displaystyle \text{slope} = RT = 291\,R \;\Rightarrow\; T = 291\ \mathrm{K} \)
\( \displaystyle t = 291 - 273 = 18\ ^\circ\mathrm{C} \)
So the osmotic pressure was measured at 18 °C.
NCERT (2026-27 edition):
Osmosis and Osmotic Pressure – “… For dilute solutions, it has been found experimentally that osmotic pressure is proportional to the molarity, C of the solution at a given temperature T. Thus: Π = CRT”