The sum of the oxidation numbers in a neutral compound is always

Zero

Explanation:

For a neutral compound I. e A compound with no net charge, the oxidation number equal as zero. This practically means that the addition of the oxidation numbers of the individual elements which are present is zero.

Conventionally, a compound is usually composed of two different parts. A net positive side and a net negative charge. Adding both of these in a neutral compound would mean that the negative charge and the positive charge canceling out. This thus leave a zero net charge on the neutral compound