Which ion has the largest radius

Which is the larger species in each pair? a. Sr or Sr²⁺ b. N or N^3- c. Ni or Ni²⁺ d. S^2- or Ca²⁺

Arrange this isoelectronic series in order of increasing atomic radius: Se^2- , Sr²⁺ , Rb⁺ , Br^- .

When electrons are added to the outermost shell of a carbon atom, it forms

Which ion has the largest radius Br^- Cl^- F^- I^-