Question -
Answer -
(a) As an atom expels a single electron, so the quantity of electron decreases by 1 but the nuclear charge does not change. Thus, the electron-electron repulsion decreases in an atom. So, there is an increase in the effective nuclear charge. Thus, there is a decrease in the radius of an atom.
(b) There is an increase in the size of an atom when it gains an electron. As it gains an electron then the quantity of electrons raises by 1. Thus, the electron-electron repulsion increases in an atom. There is an increase in effective nuclear charge as the quantity of proton remains unchanged. Thus, there is an increase in the radius of an atom.