Question

Among the following which is not a colligative property?
A. Osmotic pressure
B. Elevation of boiling point
C. Vapour pressure
D. Depression of freezing point

Answer 1

Hint- In order to deal with this question first we elaborate the term colligative property and also the criterion for a property for being a colligative property and further according to it we will see which one is not included in it.

Complete step-by-step answer:
The word "colligative" derives from the context of the Latin colligatus, linked together. This implies that all colligative properties have one specific trait, namely that they are related only to the number of solvent molecules proportional to the number of solvent molecules and not to the existence of the solvent.
Colligative properties in chemistry are those properties of solutions that depend on the ratio of the number of solvent particles to the number of solvent molecules in a solution and not on the existence of the present chemical species. The ratio of numbers can be related to the different units for solution concentration, such as molarity, molality, normality (chemistry) etc.
Colligative properties include:
Depression of freezing point
Elevation of boiling point
Osmotic pressure
Relative lowering of vapour pressure
For a given solute-solvent mass ratio, all colligative properties are inversely proportional to solute molar mass.
Hence the correct answer is option C.

Note- The statement that the properties of the solution are independent of the composition of the solvent particles is only true for perfect solutions, and is estimated for dilute actual solutions. In other words, colligative properties are a set of properties of the solution which can be accurately approximated if the solution is optimal. Colligative properties are simply liquid products that are changed by the solute presence. The solvent particles displace certain solvent molecules in the liquid phase and thus the solvent concentration, so that the colligative effects are independent of the solvent itself.