Given below are two statements on boiling point and melting point of hydrogen halides

Q. Given below are two statements :

Statement I : The increasing order of boiling point of hydrogen halides is HCl < HBr < HI < HF.

Statement II : The increasing order of melting point of hydrogen halides is HCl < HBr < HF < HI.

In the light of the above statements, choose the correct answer from the options given below :

A. Statement I is false but Statement II is true

B. Both Statement I and Statement II are false

C. Statement I is true but Statement II is false

D. Both Statement I and Statement II are true

Correct Answer: Both Statement I and Statement II are true

Solution

For hydrogen halides, boiling point depends on intermolecular forces.

HF shows strong hydrogen bonding, so it has an abnormally high boiling point compared to HCl, HBr and HI.

Among HCl, HBr and HI, boiling point increases with molecular mass due to stronger van der Waals forces.

Boiling point order: HCl < HBr < HI < HF

Hence, Statement I is true.

Melting point depends on crystal lattice packing. HI has the highest molar mass and better packing efficiency, so it has the highest melting point.

Melting point order: HCl < HBr < HF < HI

Hence, Statement II is also true.

Therefore, the correct answer is Both Statement I and Statement II are true.