Question

Chose the correct statement.
(A) The melting point of all substances decreases with an increase in pressure.
(B) The boiling point of water increases with the addition of impurities.

• A. Only (A) is correct
• B. Only (B) is correct
• C. Both (A) and (B) are correct
• D. Both (A) and (B) are incorrect

Answer 1

The correct option is B

Only (B) is correct

The explanation for the correct statement:

Option B

1. Generally, at the temperature at which boiling occurs of any solvent, has its vapour pressure is equal to its surroundings.
2. When a solute is dissolved into it, the vapour pressure decreases. So, more heat has to be supplied for the solution to make its vapour pressure equal to its surroundings.
3. Therefore, the boiling point increases by adding impurities.
4. So, (B) is the correct statement.

The explanation for the incorrect statement:

Option A

1. By increasing pressure, intermolecular forces of solid get hold more forcefully.
2. So, more heat is required to decrease intermolecular forces.
3. So, the melting point increases with increasing pressure.
4. So, (A) is incorrect.

Clearly, options C and D will also be incorrect.

Hence, the correct option is B.