Question

give scientific reason which is bigger Cl atom or Cl1- ion? why

Answer 1

Because the nucleus can't hold the 18 electrons in the Cl- ion as tightly as the 17 electrons in the neutral atom, the negative ion is significantly larger than the atom from which it forms. For the same reason, positive ions should be smaller than the atoms from which they are formed.

Answer 2

Chloride ion has a bigger atomic radius due to an increase in number of electrons