Which statement about oxidation numbers is true for a neutral molecule such as CO2?

Which statement about oxidation numbers is true for a neutral molecule such as CO2?

• A. The sum is equal to the molecule's charge.
• B. The sum is always -1.
• C. The sum is zero.
• D. The sum equals the total number of atoms.

Answer: (C)

The total of oxidation numbers must equal the overall charge of the species. For a neutral molecule like CO2, that charge is zero, so the oxidation numbers add up to zero. In CO2, each oxygen is typically assigned an oxidation state of −2, giving a total of −4 from the oxygens. To balance to zero, the carbon must be +4. Thus the sum of oxidation numbers is zero, matching the neutral charge. (Note: the general rule is that the sum equals the molecule’s charge; for a neutral molecule, that means zero, which aligns with this result.)

The total of oxidation numbers must equal the overall charge of the species. For a neutral molecule like CO2, that charge is zero, so the oxidation numbers add up to zero. In CO2, each oxygen is typically assigned an oxidation state of −2, giving a total of −4 from the oxygens. To balance to zero, the carbon must be +4. Thus the sum of oxidation numbers is zero, matching the neutral charge. (Note: the general rule is that the sum equals the molecule’s charge; for a neutral molecule, that means zero, which aligns with this result.)