To convert a mass of a substance to units of moles, we would need the molar mass of the substance since is it describes the mass of one mole of that substance. For CuCl2, the molar mass is 134.45 g/mol. For Al, the atomic mass is 26.98 g/mol.
2.50 g CuCl2 ( 1 mol / 134.45) = 0.019 mol CuCl2 0.25 g Al ( 1 mol / 26.98 g ) = 0.0093 mol Al