Question

Why do ${}_{17}^{35}Cland{}_{17}^{37}Cl$ have the same chemical properties ? In what respect do these atoms differ ?

Answer 1

Cl-35 and Cl-37 are isotopes i.e. they have same number of electrons but different number of neutrons.

Since chemical properties depends on electrons therefore isotopes have same chemical properties.

Isotopes differ by their mass number or rather the number of neutrons present in their nucleus.