Which ion is known as nitrate (NO3)?

Nitrate is represented by the chemical formula NO3 and is classified as a polyatomic ion. It has a molecular structure consisting of one nitrogen atom covalently bonded to three oxygen atoms. The overall charge of the nitrate ion is -1. This negative charge results from the fact that the nitrogen atom in the nitrate ion typically shares electrons with the oxygen atoms, leading to an excess of electrons relative to protons.

In contrast, the other charge options do not accurately reflect the characteristics of the nitrate ion. A +1 or +2 charge would indicate that the ion has lost electrons, while a -2 charge would suggest that it has gained an excessive number of electrons, which does not apply to nitrate. Hence, the charge of -1 is the defining feature of the nitrate ion, making it the correct choice.