Final answer:
Salt substitutes should only be given to renal failure patients if prescribed by a nephrologist.
Step-by-step explanation:
The answer to the question is d) Only if prescribed by a nephrologist. Salt substitutes should not be given to renal failure patients without proper guidance from a nephrologist. Patients with renal failure often have trouble excreting excess sodium from their body, which can lead to complications. Therefore, it is important for a nephrologist to prescribe the appropriate salt substitutes and monitor their usage to ensure the patient's safety and well-being.