Final answer:
The major resonance contributors for the formate anion (HCO2-) are 1) a double bond between carbon and oxygen with a negative charge on oxygen, and 2) a double bond between carbon and one oxygen atom with a negative charge on carbon.
Step-by-step explanation:
Resonance contributors for the formate anion (HCO2-) can be identified by examining the different possible arrangements of electrons. In this case, there are two major resonance contributors:
1. The first contributor has a double bond between carbon and oxygen, and a single bond between carbon and oxygen. This contributor has a negative charge on the oxygen atom.
2. The second contributor has a double bond between carbon and one of the oxygen atoms, and a single bond between carbon and the other oxygen atom. This contributor has a negative charge on the carbon atom.