NO2, the formula for the nitrite ion, carries a charge of minus 1. An ion with a negative charge, such as the nitrite ion, is known as an anion. An ion with a positive charge is known as a cation.
The charge of a NO2 ion is typically indicated with minus sign written in superscript at the end of the formula. The different charges on ions are based on the number of protons compared to the number of electrons. For example, an oxygen ion carrying a charge of minus two has two more electrons than it does protons. Protons carry a positive charge and electrons carry a negative charge.