HF is a low boiling liquid due to the presence of hydrogen bonding in the molecules. Due to hydrogen bonding in HF molecules it exist as associated molecules (HF)n . −−−H−F−−HF−−−HF−−−HF−−− or (HF)nHCl is a gas due to absence of hydrogen bonding in the molecules. Hydrogen bond is formed between H-atom and most electronegative atom (like, N, O and F).