Question

Which of the following have smaller radii than a potassium ion?

Na⁺

Rb

Cs⁺

K

Li⁺

Answer 1

Na+ and Li+ ions have smaller radii compare to K+ ion.

Because

K atomic configuration is 1s2 2s2 2p6 3s2 3p6 4s1 then K+ ion configuration will be1s2 2s2 2p6 3s2 3p6 4s0

Na atomic configuration is 1s2 2s2 2p6 3s1 then Na+ ion configuration will be 1s2 2s2 2p6 3s0

similarly Li atomic configuration is 1s2 2s1 then Li+ ion configuration will be 1s2 2s0

From the above configurations Li+ and Na+ ions have on orbit lesser than K+ ion hence both are less atomic radii compare to K+ ion