Which of these ions contains 4n π electrons?

Question

Which of these ions contains  4n π electrons?

Quizplus · Accepted Answer

Iodide ion (I-) has 4n π electrons because it has a lone pair of electrons which forms a π bond with the adjacent σ bond. This results in a total of 4n π electrons.
Nitrate ion (NO3-) has 3 resonance structures, each with a double bond and a single bond. This leads to a total of 6 π electrons. Therefore, it does not have 4n π electrons.
Carbonate ion (CO32-) also has 3 resonance structures, but two have double bonds and one has a single bond. This leads to a total of 4 π electrons. Therefore, it also does not have 4n π electrons.
So, the correct answer is D as only I and III (Iodide and Carbonate ion) have 4n π electrons.

Which of These Ions Contains 4n π Electrons