(i) K is larger in size than K⁺ . The electronic configuration of K and K⁺ are:

K ∶ 1s² , 2s²2p⁶ ,3s²3p⁶ ,4s¹

K⁺ ∶ 1s² , 2s²2p⁶ , 3s²3p⁶,

K⁺ is formed from K when the later loses its 4 electrons.

K → K⁺ + e⁻

As seen from the electronic configurations of K and K⁺ , the K⁺ ion has 18 electrons and K atom has 19 electrons but the nuclear charge in both these species is the same (+ 19). Since K⁺ ion has 1 electron less than K atom, the forces of attraction between the nucleus and the electrons are more strong in K⁺ ion than in K atom. This results in more inward pulling of electrons towards the nucleus in K⁺ ion and hence its size decreases.

(ii) Bris formed by the gain of one electron by Br atom. In Br^- the nuclear charge is the same as that in the Br atom but the number of electrons has increased. Since same nuclear charge now acts on increased number of electrons, the effective nuclear charge per electron decreases in Br^-. The electron cloud is held less tightly by the nucleus. This causes increase in the size.