Oxidizing Nature of Sulphuric Acid

Q. The variation of the boiling points of the hydrogen halides is in the order $HF>HI>HBr>HCl$
What explains the higher boiling point of hydrogen fluoride?

1. There is strong hydrogen bonding between HF molecules.
2. The bond energy of HF molecules is greater than in other hydrogen halides.
3. The effect of nuclear shielding is much reduced in fluorine which polarises the HF molecule.
4. The electronegativity of fluorine is much higher than for other elements in the group.