Compare the radii of two species X and Y. Give reasons for your answer.
(a) X has 12 protons and 12 electrons
(b) Y has 12 protons and 10 electrons
The available information makes it clear that :
(a) Species X with equal number of protons (12) and electrons (12) is an atom.
(b) Species Y with two electrons less (10) than the number of protons (12), is a divalent cation y2+ of species X.
Therefore, the radius of species X is more as compared to that of y2+.
Note : The radius of cation is always less than that of atom while that of anion is more.