Which of the following is the correct order of size of the given species:
(i) I > I- > I+
(ii) I+ > I- > I
(iii) I > I+ > I-
(iv) I- > I > I+
The answer is the option (iv) I- > I > I+
Explanation: A cation is always smaller in size than its parent atom because in case of cations there are fewer electrons in it than its parent atom, but the nuclear charge is same in both; thus there is a greater pull towards the nucleus thereby reducing the size of the cation. The opposite happens in case of an anion where the nuclear charge remains the same, but the number of electrons is increased by one or more than the parent atom, and this results into increased repulsions among electrons and thus causes a decrease in effective nuclear charge, and as a result, the size of the anion increases manifold.