Oxygen has an atomic number of 8. the n = 1 energy level has two electrons, and the n = 2 energy level has six electrons. oxygen's valence is +2 -2 +1 -1

Valence is defined as number of electrons that are present in the outermost orbital. Oxygen is in the 16th column of the periodic table and the total number of valance electrons is determined by units place digit of the column position which is 6 for oxygen. The outermost orbital is the high energy level and there are two in that orbit. So the valance is +2.

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