Final answer:
The substance that will be least effectively separated from acetic acid via distillation is CH2ClCH2OH.
Step-by-step explanation:
In distillation, a method used to separate mixtures, the substances with different boiling points are vaporized and then condensed back into their liquid form. The substance that will be least effectively separated from acetic acid via distillation is the one that has a boiling point close to that of acetic acid, as it will have similar vaporization and condensation properties. Therefore, the molecule that is least effectively separated from acetic acid is D. CH2ClCH2OH because it has a boiling point closest to that of acetic acid.