The sum of bond order of $\mathrm{O}_2^{+}, \mathrm{O}_2^{-}, \mathrm{O}_2$ and $\mathrm{O}_2^{2+}$ is equal to

• A

  $5$
• B

  $4$
• C

  $6$
• Correct answer
  D

  $9$

Hence, the correct answer is option: 'D'.