Here's how to determine the simplest formula (empirical formula) of the copper oxide:

1. Find the mass of oxygen:

* Mass of oxygen = Mass of copper oxide - Mass of copper

* Mass of oxygen = 2.81 g - 2.50 g = 0.31 g

2. Convert masses to moles:

* Moles of copper = (2.50 g Cu) / (63.55 g/mol Cu) = 0.0393 mol Cu

* Moles of oxygen = (0.31 g O) / (16.00 g/mol O) = 0.0194 mol O

3. Determine the mole ratio:

* Divide the number of moles of each element by the smallest number of moles:

* Cu: 0.0393 mol / 0.0194 mol = 2.02 ≈ 2

* O: 0.0194 mol / 0.0194 mol = 1

4. Write the empirical formula:

* The simplest formula of the copper oxide is Cu₂O.

Therefore, the simplest formula of the copper oxide is Cu₂O. This corresponds to copper(I) oxide.