What is the correct formula for nitrate?

Nitrate is a polyatomic ion with the chemical formula NO₃⁻. This indicates that it consists of one nitrogen atom (N) and three oxygen atoms (O) and carries a net negative charge of one, which is represented by the superscript negative sign.

The reason this formula is correct is rooted in the structure and charge of nitrate. It is important to recognize that the total number of valence electrons in the ion leads to its negative charge. In this case, nitrogen contributes five valence electrons, and each oxygen contributes six, totaling 23 electrons. To achieve a stable configuration, an additional electron gives nitrate a total of 24 electrons, which corresponds to the negative charge.

Other options present incorrect formulas or indicate different ions. For instance, NO₃²⁻ suggests a charge of two negative, which does not apply to nitrate. Similarly, NO₂⁻ refers to the nitrite ion, which has one less oxygen atom than nitrate and also carries a single negative charge but represents a different chemical species entirely. Finally, NO₄⁻ indicates a fictitious ion as there is no recognized nitrate equivalent with four oxygen atoms possessing a single negative charge. Therefore, NO₃⁻ accurately identifies nitrate, making