Why are hydrogen halides and not halogen acids preferred for preparing haloalkanes from alkenes?

Explanation

This may be illustrated by the addition of both these compounds to propene.
Hydrogen halide. This represents the gaseous state of HX which means that no water is present.

Halogen acid. It represents the aqueous solution of HXgt Here both `X^(-)` ion and `H_(2)O` molecule can combine with the carbocation formed in the slow step.

Thus, a mixture of haloalkane and alcohol will be formed in this case. that is why, hydrogen halide is preferred.