1. Meaning of negative deviation from Raoult’s law

For an ideal solution, Raoult’s law predicts the vapour pressure directly from mole fractions.
If a solution shows negative deviation, then its actual vapour pressure is less than the value predicted by Raoult’s law.

This happens when the intermolecular attraction between unlike molecules, say $A-B$, is stronger than the attractions $A-A$ and $B-B$.

So, compared to an ideal solution: $P_{\text{actual}} < P_{\text{Raoult}}$

Hence, the solution has decreased vapour pressure.

2. Effect on boiling point

A liquid boils when its vapour pressure becomes equal to atmospheric pressure.

If the vapour pressure is lower, then the liquid must be heated to a higher temperature to reach atmospheric pressure.

Therefore, a solution showing negative deviation from Raoult’s law has:

• lower vapour pressure
• higher boiling point

3. Check the options

• A: increased vapour pressure, increased boiling point  incorrect
• B: increased vapour pressure, decreased boiling point  incorrect
• C: decreased vapour pressure, decreased boiling point  incorrect
• D: decreased vapour pressure, increased boiling point $\checkmark$ correct

4. Final answer

A solution showing negative deviation from Raoult’s law has decreased vapour pressure and increased boiling point.