[sn1sn2e1e2]

The radius of which ion is closed to that of the Li+ ion?

(A) Na+

(B) Be2+

(C) Mg2+

(D) Al 3+

I chose (B) but the answer is (C)

My reasoning is that Mg2+ Zeff charge is strong enough to pull all its electrons to match Li+'s. But how do you know that Mg2+ nuclear charge is similar to Li+ than Be2+? In Be2+, you only remove 2 electrons so shouldn't it be close to Li+?

[cheah10]

it seems that generally when an electron is removed from an atom, the size of the remaining ion shrinks quite significantly, don't you think so? take a look at this picture and compare the radii:
http://upload.wikimedia.org/wikipedia/commons/thumb/9/9f/Atomic_%26_ionic_radii.svg/996px-Atomic_%26_ionic_radii.svg.png