Which of the following haloalkanes exist as liquids at room temperature?

Propyl bromide

The answer is (3). Propyl bromide exists as a liquid at room temperature. The other haloalkanes listed are gases at room temperature.

The boiling point of a haloalkane is determined by the size of the alkyl group and the strength of the intermolecular forces. The larger the alkyl group, the higher the boiling point. The stronger the intermolecular forces, the higher the boiling point.

Propyl bromide has a larger alkyl group than methyl chloride or methyl bromide. Propyl bromide also has stronger intermolecular forces than ethyl chloride. Therefore, propyl bromide has the highest boiling point and exists as a liquid at room temperature.

Here is a table of the boiling points of the haloalkanes listed: