Question

What is the oxidation number of the `Ni` atom in `Ni_3(PO_4)_2`?

Answer 1

We first work out the charge of the `PO_4`-group.

Explanation:

`P` can be either `+3or+5`
In this case it must be `+5` or it wouldn't work out with the rest.

So `PO_4=+5+4*(-2)=-3`, so it's `PO_4^(3-)`

There are 2 `PO_4^(3-)`'s for a total charge of `-6`

To balance that, the three `Ni`'s must have a charge of `+2` each.

So the oxidation number is `Ni^(2+)`