Explain why a hydrogen bond between two water molecules is weaker than a hydrogen bond between two hydrogen fluoride molecules.

The hydrogen bond between hydrogen fluoride molecules is stronger because the polarization in H-F molecule is stronger.

Explanation:

The more polarization happens in the molecule the stronger the inter-molecular hydrogen bond is.

Consider water (H - O - H) and hydrogen fluoride (H - F), the polarization of the (H - F) bond is stronger than the (O - H) bond due to the higher electronegativity of the fluoride atom. Actually, fluoride has the highest electronegativity.