Why do isomers have different properties let it be chemical or physical?

Answer 1

First, consider the definition of an isomer.

An isomer is a chemical species with the same number and types of atoms as another chemical species but with distinct properties because the atoms are arranged into different chemical structures.

The fact that the atoms are arranged into different chemical structures help to explain why they have different chemical and/or physical properties. They are different and so you might expect them to behave differently.