To find the empirical formula, we need to determine the simplest whole number ratio of the elements present in the compound. Let's assume we have 1 mole of H2C2O4. This means we have:

- 2 moles of H atoms

- 2 moles of C atoms

- 4 moles of O atoms

Now, we calculate the relative number of each element by dividing the number of moles of that element by the smallest number of moles. In this case, the smallest number of moles is 2 (for H):

- H: (2 moles) / 2 = 1

- C: (2 moles) / 2 = 1

- O: (4 moles) / 2 = 2

So, the empirical formula of H2C2O4 is CH2O2.