1. Start by assigning the oxidation number of oxygen as -2, as it is a common convention.
2. Since there are four oxygen atoms in the phosphate (PO₄) group, the total negative charge contributed by oxygen is -8.
3. The overall compound is neutral, so the sum of the oxidation numbers of Cobalt (Co) and the phosphate group must be zero.
4. Let x represent the oxidation number of Cobalt (Co). Then we can set up the equation: x + (-8) = 0.
5. Solving for x, we get x = +8.
Therefore, the oxidation number of Cobalt (Co) in Cobalt III Phosphate is +3.
