Answer:
1. The oxidation number of a free element is always 0.
2. The oxidation number of a monatomic ion equals the charge of the ion.
3. The oxidation number of H is +1, but it is -1 in when combined with less electronegative elements.
4. The oxidation number of O in compounds is usually -2, but it is -1 in peroxides.
Explanation:
