Q. 354.4( 7 Votes )

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 :

Radii of Y is less than X.


Here, X has 12 electrons and 12 protons, therefore it is a neutral atom. Y contains 12 protons and 10 electrons so there are 2 more protons that gives Y a charge of +2. The electronic configurations of the two species is as follows:



The atomic size of a positive ion (cation) is always smaller than a neutral atom. This is because cation has less number of electrons and hence more nuclear attractions on electrons in cation. Thus the size of a cation is smaller than that of the neutral atom. Hence, atomic radius of Y is smaller than that of X.


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