Question

Which of the following is the correct decreasing order of boiling points?

• A. $HF>HI>HBr>HCl$
• B. $HF>HBr>HI>HCl$
• C. $HCl>HBr>HI>HF$
• D. $HCl>HI>HBr>HF$

Answer 1

The correct option is A $HF>HI>HBr>HCl$

The boiling point of a compound depends on its intermolecular interactions.
When the molecule has an electronegative atom, it develops charges which leads to hydrogen bonding.
Higher the electronegativity, stronger is the bond and hence higher is the boiling point.
$HF$ has strong hydrogen bonding, whereas the others which are gases have weak van der Waals force and thus, $HF$ has the highest boiling point.
Since, other halogens do not show hydrogen bonding, the boiling point is determined by the molecular weight. They have van der Waals force of attraction. van der Waals force increases with increase in atomic or molecular mass and so the correct order of decreasing boiling points is given below: $HF>HI>HBr>HCl$.