The radius of hydrogen atom in the ground state is 0.53 A°, the radius of Li²⁺ in the similar state is

The radius of H-atom in the ground state is 0.53 A⁰

The radius of Li²⁺ ion in the ground state is  (r )= 0.529 $\times$n²/Z

 (r) = 0.529 $\times$1² /3

 (r) =0.716 A⁰