In carbon dioxide, what are the oxidation numbers of carbon and oxygen?

• A. C +2, O -2
• B. C +4, O -2
• C. C 0, O 0
• D. C -4, O +2

Answer: (B)

The key idea is balancing oxidation numbers in a neutral molecule using the rule that the sum must be zero, and knowing that oxygen is more electronegative than carbon, so it carries the electrons. In carbon dioxide there are two oxygens, each with an oxidation number of -2, giving a total of -4 from oxygen. To balance to zero, the carbon must contribute +4. So the oxidation state is carbon +4 and each oxygen -2. This fits because +4 plus two times -2 equals zero. The other options don’t balance to zero or assign unlikely charges to oxygen based on electronegativity.