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MCAT Question A Day - 10/23/14 - Answer!

Which of the following species has an unpaired electroin its ground-state electronic configuration?

A.  Ne
B.  Ca+
C.  Na+
D.  O2-

B is correct. The quickest way to see this is by realizing that atoms like to form ions with electron configurations similar to the nearest noble gas. Of course a noble gas does not have any unpaired electrons. You should recognize that Ca likes to form a 2+ ion not a 1+ ion.

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