Boiling points of hydrogen halides follow which order?

Observed boiling points (°C): HF +19.5, HCl -85, HBr -67, HI -35. Ordering: $\mathbf{HF > HI > HBr > HCl}$. **HF is anomalously high** because of strong hydrogen bonding (F is highly electronegative and small, the H-F-H interaction is strong). HCl < HBr < HI follows the usual molecular-mass trend (heavier = higher BP because of larger London dispersion forces). HF jumps above all three by virtue of H-bonding. Same pattern explains why water has higher BP than $\mathrm{H_2S}$, $\mathrm{H_2Se}$, $\mathrm{H_2Te}$ — H-bonding via the strongly electronegative O.