Final answer:
The client with Addison's disease is at the highest risk for hyperkalemia because the condition can lead to decreased excretion of potassium by the kidneys (c).
Step-by-step explanation:
The nurse should assess the client with Addison's disease most carefully for the development of hyperkalemia. Addison's disease is a condition where the adrenal glands do not produce sufficient steroid hormones, including aldosterone, which helps regulate potassium levels.
Without enough aldosterone, the kidneys may excrete too much sodium and not enough potassium, leading to an accumulation of potassium in the blood, hence hyperkalemia. Therefore, clients with Addison's disease are at a higher risk for developing hyperkalemia due to decreased excretion of potassium by the kidney.