Question

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

Answer 1

From electron arrangement
X -- 2.8.2
Y -- 2.8

Since Y has fewer energy levels it's atomic radius will be smaller than that of X.

Note:
X and Y have the same no. of protons
Y is actually an ion of X obtained when X loses the two electrons in its outermost energy level.

Answer 2

Answer:X is bigger and Y is smaller

Explanation: as there are more shells in X (2 ,8,2) the effective nuclear charge is less.hence it is smaller in size

And ther is less no. Of shells in Y (2,8) so the effective nuclear charge is more.hence it is bigger in size.