What do you mean by "Isotopic effect" ?

Explanation

All the three isotopes of hydrogen have the same atomic number and similar electronic configuration `(1s^1)` . Due to same electronic configuration, they have similar chemical properties. But as their atomic mass differs, the rate constants of their reactions differ. Therefore, the isotopes of hydrogen have different physical properties. Thus, the difference in properties due to the difference in their atomic masses is called "Isotopic effect".