What is the maximum and minimum oxidation number of oxygen?

Answer 1

As an element, magnesium has an oxidation number of zero - it has control of it's own electrons, no more, no less.

When it reacts, it gives away two electrons and becomes a 2+ ion. It therefore has an oxidation number of +2.

All elements have an oxidation number of 0.

In compounds;

Everything in group 1 will take an oxidation number of +1.

Everything in group 2 will take an oxidation number of +2.

Halides generally have oxidation numbers of -1 but chlorine has many possibilities.

Hydrogen is generally +1 but can be -1 if combined with a metal.

Oxygen is always -2.

You work out the oxidation numbers of other things using these, for example, in the ion NO3- each oxygen is -2, there are three of them, making -6.

The overall ion is -1, so the N must be +5.This doesn't mean it is an ion that has lost 5 electrons, it means that it has given away control of 5 electrons to the oxygens that it is covalently bonded with.

Answer 2

The oxidation number of oxygen can go from -2 to +2.
The highest is therefore +2 and the lowest is -2