Right answer is (a) Nitrogenous wastes
The best explanation: Nitrogenous wastes are not present in the dialysing fluid. The dialysing unit after the addition of an anticoagulant like heparin contains a coiled cellophane tube surrounded by a fluid which proteins, electrolytes and glucose (almost same as that of the plasma) except for the fact that it does not have nitrogenous wastes.