Discussion
The CORRECT order of boiling points for the hydrogen halides is
Answer: A
The order is HF \(\gt\) HI \(\gt\) HBr \(\gt\) HCl.
HF boils far higher than the others (about 20 °C) because its molecules are linked by strong hydrogen bonds, F being small and highly electronegative. Among HCl, HBr and HI hydrogen bonding is negligible, and boiling point rises with molar mass and polarisability, because London dispersion forces grow with the size of the electron cloud: HI (about -35 °C) \(\gt\) HBr (about -67 °C) \(\gt\) HCl (about -85 °C).
HF \(\gt\) HCl \(\gt\) HBr \(\gt\) HI reverses the dispersion trend. HI \(\gt\) HBr \(\gt\) HCl \(\gt\) HF ignores hydrogen bonding in HF. HI \(\gt\) HF puts HI above HF, which understates the effect of hydrogen bonding.
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