The question is asking about the oxidation number of the compound CaC₂O₄, which is calcium oxalate. It's not possible to assign an oxidation number to an entire compound. Oxidation numbers are assigned to individual elements within a compound.

Here's how we can figure out the oxidation numbers of the individual elements in CaC₂O₄:

* Calcium (Ca): Calcium is in group 2 of the periodic table, so it always has an oxidation number of +2 in its compounds.

* Carbon (C): The oxalate ion (C₂O₄²⁻) has a charge of -2. Oxygen typically has an oxidation number of -2, and there are four oxygen atoms, giving a total of -8. To balance the -2 charge of the ion, each carbon atom must have an oxidation number of +3.

* Oxygen (O): As mentioned above, oxygen typically has an oxidation number of -2 in compounds.

Summary of Oxidation Numbers in CaC₂O₄:

* Ca: +2

* C: +3

* O: -2