Question

Among S^2-, Cl^-, Ar, K⁺, Ca²⁺, Se^2-, Br^-, Kr, Rb⁺, and Sr²⁺, which one has the largest radius?

Answer 1

Ionic radii decreases as increasing positive charge and increases as increasing negative charge.

As we go down the group and along the period the ionic radii increases

S^{​​​​​2-} , Cl^{​​​​​-} , Ar, K^{​​​​​​+} , Ca^{​​​​​2+} all have same electronic Configuration as Ar. And in these S^{​​​​​​2-}​ have more negative charge. Hence in this S^{​​​​​2-} has largest radius among them.

Same as above among Se-2, Br-, Kr, Rb⁺, Sr^{​​​​​2+} , Se^{​​​​​-2} has largest radius among them.

Among S^{​​​​​​2-} and Se^{​​​​​-2} , Se^{​​​​​-2} has largest radius because as we go down the group size increases.

Hence, Se^{​​​​​-2} is the correct answer.