Consider the following statements about solutions of solids in liquids.
(A) In a solution of a non-volatile solute, the fraction of the surface covered by the solvent molecules gets increased.
(B) The decrease in the vapour pressure of water by adding 1.0 mol of sucrose to one kg of water is nearly similar to that produced by adding 1.0 mol of urea to the same quantity of water at the same temperature.
(C) Iodine and sulphur dissolved in carbon disulphide are examples of solutions of solids in liquids.
(D) Raoult’s law in its general form states that, for any solution, the partial vapour pressure of each volatile component in the solution is directly proportional to its molality.
Which of the statements given above are incorrect? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A) and (D) only
When a non-volatile solute is dissolved in a liquid, the solute particles take up part of the surface. Fewer solvent molecules can escape, so the vapour pressure falls, and the fall depends on how much solute is present, not on what it is.
(A) In a solution of a non-volatile solute, the fraction of the surface covered by the solvent molecules gets increased. — Incorrect statement. The surface now has both solute and solvent molecules, so the fraction covered by the solvent molecules is reduced, not increased.
(B) The decrease in the vapour pressure of water by adding 1.0 mol of sucrose to one kg of water is nearly similar to that produced by adding 1.0 mol of urea to the same quantity of water at the same temperature. — Correct statement. The lowering depends on the quantity of the non-volatile solute, irrespective of its nature, and both solutions have the same amount of solute.
(C) Iodine and sulphur dissolved in carbon disulphide are examples of solutions of solids in liquids. — Correct statement. Iodine and sulphur are solids and carbon disulphide is the liquid solvent.
(D) Raoult’s law in its general form states that, for any solution, the partial vapour pressure of each volatile component in the solution is directly proportional to its molality. — Incorrect statement. Raoult’s law relates the partial vapour pressure to the mole fraction of the component, not to its molality.
NCERT (2026-27 edition):
1.4.3 Vapour Pressure of Solutions of Solids in Liquids – “Another important class of solutions consists of solids dissolved in liquid, for example, sodium chloride, glucose, urea and cane sugar in water and iodine and sulphur dissolved in carbon disulphide.”
“…In the solution, the surface has both solute and solvent molecules; thereby the fraction of the surface covered by the solvent molecules gets reduced. Consequently, the number of solvent molecules escaping from the surface is correspondingly reduced, thus, the vapour pressure is also reduced.”
“The decrease in the vapour pressure of solvent depends on the quantity of non-volatile solute present in the solution, irrespective of its nature. For example, decrease in the vapour pressure of water by adding 1.0 mol of sucrose to one kg of water is nearly similar to that produced by adding 1.0 mol of urea to the same quantity of water at the same temperature.”
“Raoult’s law in its general form can be stated as, for any solution the partial vapour pressure of each volatile component in the solution is directly proportional to its mole fraction.”