One mole electron means:

1 electron weighs approximately 9.11×10−31 Kg 1 mol weighs X Kg 1 mol is 6.022×1023 particles So we put 6.022×1023 in the equation instead. X=9.11×10-311×6.023×1023 =5.48×10-7kg​∴ mass of one electron =0.548mg ≈ 0.55mg