Answer:The correct answer is :'because they have different boiling points'.
Step-by-step explanation:
Isomers are those molecules with with same molecular formula but different structural formula.They have different atomic arrangement due to which there boiling point differ with one another.
For example: Butane as higher boiling point than 2 methyl propane because due to branching the boiling point of an hydrocarbon decreases.
Since they differ in boiling points thy can be easily separated from each other by the distillation process.
The principle behind the distillation process is the different liquids boils at different temperature.