The formula Fe5O5 represents one formula unit of the compound iron(III) oxide-hydroxide. To determine the total number of atoms in one formula unit, we need to count the number of atoms of each element present in the formula.

- Iron (Fe): The formula contains five iron (Fe) atoms.

- Oxygen (O): The formula contains five oxygen (O) atoms.

Therefore, one formula unit of Fe5O5 contains a total of 5 + 5 = 10 atoms.