Dear han i,
The chemical reactivity of the Isotopes are nearly the same because they have the same number of electrons which in turn are controlled by the number of protons in a neutral atom !
But remember that Neutrons also play a small role in determining the chemical reactivity of Isotopes !
The More the number of Neutrons then the chemical reacitivity of the Isotope decrease while the chemical reactivity increease with the decrease in the number of Neutrons !!
Hope you understood it now..
All the Best & Good Luck !!
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