X and Y are two elements. X has 12 protons and 12 electrons. Y has 12 protons and 10 electrons. What among the following statements about their atomic radius is true?

X has 12 protons and 12 electrons so; it is electrically neutral. Y has 12 protons and 10 electrons so; it is a cation and has +2 charge on it. 

We know that cations are always smaller than their respective neutral atoms. This is because cations have a higher effective nuclear charge exerted on their valence electrons as compared to that of neutral atoms. 

Hence, the atomic radius of X is greater than the atomic radius of Y.