Which electron configuration represents the electrons of an atom in an excited state?
(1) 2-1
(3) 2-8-7
(2) 2-7-4
(4) 2-4

3) 2-8-7

Explanation:

An atom is in an excited state when it is very close to having a full octet (either it gains or loeses electrons to get a full octet). The first shell should have two electrons and the next one and the one after that should be eight. Since the third shell has 7 electrons it needs to gain one more electron to get a full octet. Therefore the answer is 3

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