Which of the following statements about the resonance structures of the formate ion (${\mathrm{HCO}}_{-}$) is correct?

• A. The resonance structures differ in the position of the hydrogen atom.
• B. The negative charge is delocalized equally between the two oxygen atoms in the resonance structures.
• C. One resonance structure has a double bond between carbon and hydrogen.
• D. The carbon atom in all resonance structures has a formal charge of $-1$.

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the structure of the formate ion (HCO\textsuperscript{−}). It consists of a carbon atom bonded to one hydrogen atom and two oxygen atoms, with an overall negative charge.
2. Step 2: Identify the resonance structures by moving electrons, not atoms. Resonance structures differ in the placement of electrons (such as pi bonds and lone pairs), but the positions of atoms, including hydrogen, remain fixed.
3. Step 3: Draw the resonance forms by shifting the double bond between carbon and one oxygen to the other oxygen, showing the negative charge delocalized between the two oxygens. This means the negative charge is shared equally between the two oxygen atoms.
4. Step 4: Check the formal charges in each resonance structure. The carbon atom typically has a formal charge of zero because it forms four bonds (one to hydrogen and three to oxygens through single and double bonds), while the negative charge is localized on the oxygens.
5. Step 5: Conclude that the correct statement is that the negative charge is delocalized equally between the two oxygen atoms, and that the resonance structures do not involve moving the hydrogen atom or placing a double bond between carbon and hydrogen.