Why not aromatic substitution reaction?

Hy .Here is your answer
Nucleophilic aromatic substitution. A nucleophilic aromatic substitution is a substitution reaction in organic chemistry in which the nucleophile displaces a good leaving group, such as a halide, on an aromatic ring.

Isotopes   are atoms of the same  element   having different atomic mass but same atomic number. for e.g., there are three  isotopes   of hydrogen with atomic mass 1, 2, and 3. according to  mendeleev's periodic table   these should be placed at three separate places.