Which of the following correctly states the relationship between oxidation number and charge for ions?

The relationship between oxidation number and charge for ions is accurately stated by the understanding that the oxidation number of an ion is indeed equal to its charge.

For example, when you consider a sodium ion (Na⁺), it has a charge of +1, and its oxidation number is also +1. In the case of a chloride ion (Cl⁻), it has a charge of -1, matching its oxidation number of -1. This consistency holds true for any ionic species.

The oxidation number reflects the hypothetical charge an atom would have if all bonds were ionic, which is precisely what happens with ions, where the charge directly corresponds to the loss or gain of electrons. Positive oxidation numbers indicate that electrons have been lost (oxidation), while negative oxidation numbers indicate that electrons have been gained (reduction).

Thus, the correct response highlights this straightforward and essential relationship, reinforcing that the oxidation number and ionic charge are quantitatively the same for simple ions.