Question

Statement I : BP order is HI<HBr<HCl<HF.
Statement II : MP order is HI<HF<HCl<HBr.

• A. Statement I and Statement II are correct
• B. Statement I is correct and Statement II is wrong
• C. Statement I is wrong and Statement II is correct
• D. Both Statement I and Statement II are incorrect

Hint:

For hydrides of groups 15, 16, and 17, always remember that the first member (NH$_3$, H$_2$O, HF) has an unexpectedly high boiling point due to hydrogen bonding.
For the others, the trend follows the increase in molecular weight.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question tests the trends in physical properties (Boiling Point - BP and Melting Point - MP) of hydrogen halides (HF, HCl, HBr, HI).
Step 3: Detailed Explanation:
Analysis of Statement I (Boiling Point):
Normally, boiling point increases with molecular mass due to increasing Van der Waals forces ($HCl<HBr<HI$).
However, $HF$ has strong intermolecular hydrogen bonding, which gives it an exceptionally high boiling point.
Correct BP order: $HCl<HBr<HI<HF$.
Statement I says $HI<HBr<HCl<HF$, which is incorrect.
Analysis of Statement II (Melting Point):
Melting point depends on both molecular mass and lattice structure.
Correct MP order: $HCl<HBr<HF<HI$.
The values are roughly: HCl (-114$^{\circ}$C), HBr (-87$^{\circ}$C), HF (-83$^{\circ}$C), HI (-51$^{\circ}$C).
Statement II says $HI<HF<HCl<HBr$, which is incorrect.
Step 4: Final Answer:
Both statements are incorrect.