Cobalt (Co) has a common oxidation number of +2. This means that it typically loses two electrons to form a cation with a charge of +2.

However, cobalt can also exhibit other oxidation states, such as:

* +3: This is less common than +2, but it's still important to know.

* +1: This is even less common, but it exists in certain compounds.

The specific oxidation state of cobalt in a compound depends on the other elements present and the structure of the compound.