Question

The vapour pressure of 4 different substances at $30{}^{0}C$ is given in the table, which statement about these are incorrect?

Substance	Vapor pressure
A	$0.0012\text{mmHg}$
B	$18\text{mmHg}$
C	$175\text{mmHg}$
D	$442\text{mmHg}$

• A. The normal boiling point of D should be greater than that of B
• B. The heat of vaporisation of C should be greater than that of B
• C. The intermolecular forces between molecules of B should be greater than those between molecules of A
• D. The surface tension of B should be greater than that of C

Answer 1

Answer: (A), (B), (C)

The intermolecular forces between molecules of B should be greater than those between molecules of A

Since vapour pressure of B is less than that of D, thus boiling point of B will be more.
The heat of vaporisation is the the amount of energy needed to change one gram of a liquid substance to a gas at constant temperature. Since vapour pressure of B is less than that of C, thus the heat of vaporisation of B is more.
More is the extent of the intermolecular forces, lesser will be the vapour pressure. Since vapour pressure of A is less than B, thus intermolecular forces between molecules of B is less than those between molecules of A.
Surface tension of $B$ would be greater than that of $C$, because vapour pressure increases due to weakening of the intermolecular forces and thus surface tension decreases.