The relative formula mass (RFM) of copper sulfate (CuSO₄) is calculated by adding the atomic masses of each element in the compound, taking into account the number of atoms of each element.

Here's the breakdown:

* Copper (Cu): 63.55 g/mol

* Sulfur (S): 32.06 g/mol

* Oxygen (O): 16.00 g/mol (and there are 4 oxygen atoms)

Therefore, the RFM of copper sulfate is:

63.55 + 32.06 + (16.00 x 4) = 159.61 g/mol