Which electron configuration represents an atom of selenium in an excited state?

2-7-18-7

Excited-state configurations have the same number of electrons as the ground-state electron configuration shown on the Periodic Table, but you DO NOT have the same number of electrons in each level as the ground-state electron configuration does. The most useful approach for this question is to add up the number of electrons in the configuration to find if it matches the element of interest, based on the atomic number. If it DOES match the atomic number, then compare it to the ground-state configuration on the Periodic Table to see if it matches. If it does NOT match the ground-state configuration, but has the same total number of electrons, it is an excited-state configuration. Also, note that the 2n^2 rule can NEVER be exceeded. Choices like 2-7-19-13-1 and 2-6-19-14-1 exceed the 2n^2 rule for n=3, where the maximum number of electrons in the n=3 level is 2(3)^2=18.