Which is NOT a valid resonance contributor of acetamide?

Given the structure of $O_3$ (ozone) as $O=O-O$, which of the following is a correct resonance structure?

Which of the following best describes the resonance hybrid of the acetate ion ${\mathrm{CH}}_3{\mathrm{COO}}_{-}$?

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

Which of the following correctly represents a valid resonance structure for the cyanate ion $C_N{-}^1$ ($\mathrm{CNO}-$)?

For each pair of ions, determine which ion is more stable. Use resonance forms to explain your answers.

(e)

(f)