ANSWER:
Chemical properties depend upon atomic number, i.e., the number of protons or the number of electrons and their arrangement in valence shells. Since, isotopes have same atomic number, they have same chemical properties.
Physical properties depend upon atomic masses or mass numbers i.e., the number of protons and neutrons. Since, isotopes have different atomic masses, they have different physical properties.
(Ref. An Insight Into Objective Chemsitry-11, Ch-01, Q. No. 17)