In OF2, what is the oxidation state of oxygen?

• A. -2
• B. +2
• C. 0
• D. +1

Answer: (B)

In a neutral compound, the oxidation numbers must add up to zero, and more electronegative elements in bonds take the electrons, giving them a negative oxidation state. Fluorine is more electronegative than oxygen, so in each O–F bond the electrons are assigned to fluorine, giving fluorine an oxidation state of −1. With two fluorine atoms, the total from fluorine is −2. To balance to zero in OF2, oxygen must have a +2 oxidation state.

Oxygen is often −2 in many compounds, but when bonded to the highly electronegative fluorine, it can become positive to balance the overall charge. If oxygen were −2, the sum would be −4; if it were 0, the sum would be −2; if it were +1, the sum would be −1. None of these balance to zero, so +2 is the correct assignment.

Therefore, the oxidation state of oxygen in OF2 is +2.