What is the formula for nitrate?

The formula for nitrate is indeed NO3-. Nitrate is the polyatomic ion that consists of one nitrogen atom (N) covalently bonded to three oxygen atoms (O), and it carries a -1 charge. This structure gives nitrate its characteristic as an important ion in various chemical reactions, particularly in organic chemistry and biochemistry, where it plays a role in nitrogen cycling.

The other options represent different ions. For instance, NO2- is the nitrite ion, which has one fewer oxygen atom than nitrate. OH- is the hydroxide ion, known for its role in basic solutions, while CO3^2- is the carbonate ion, which contains carbon and three oxygen atoms, carrying a -2 charge. Each of these ions has distinct structures and functions in chemical reactions, making them different from the nitrate ion.