C) HF, because it has the strongest intermolecular force
Explanation:
The electronegativity difference ΔEN between H and F is so high that HF has especially high dipole-dipole forces, which we call hydrogen bonds. They are the strongest intermolecular forces, and they are responsible for the high boiling point of HF.
A) is wrong. HI has a higher mass and more electrons than HBr.
B) is wrong. There is no hydrogen bonding in HCl.
D) is wrong. There are no ion-dipole forces in HI.
