* Rules to Remember:
* The oxidation number of an element in its elemental form is 0.
* The oxidation number of oxygen is usually -2, except in peroxides (like H₂O₂) where it is -1.
* The oxidation number of sulfur is usually -2, except in certain compounds.
* The sum of the oxidation numbers in a neutral compound is 0.
* Applying the Rules:
* We know the oxidation number of sulfur (S) is -2.
* The compound CoS is neutral, meaning the sum of the oxidation numbers must be 0.
* Therefore, the oxidation number of cobalt (Co) must be +2 to balance the -2 from the sulfur.
So, the oxidation number of Co in CoS is +2.
