Praxis II: Chemistry Exam Prep

Answer: D. The Lewis diagram shows Nitrogen at the center with two single bonds to two of the oxygen’s and a double bond to the third. The formal charge is calculated with the following equation:

Formal charge = (valence electrons) - (1/2 bonding electrons) - (lone electrons)
Formal charge = (5) -(1.2 * 8) - (0)
Formal charge = +1

NO₃^- as a compound has a formal charge of -1. This is because the oxygen atom in the double bond has a formal charge of 0, and the other two electrons have a formal charge of -1. The total charge is then: 1 + 0 - 1 - 1 = -1.