Final answer:
The nurse should monitor for postural hypotension in a client prescribed a nonselective beta-blocking agent.
Step-by-step explanation:
The adverse effect that the nurse should monitor for in a client who has been prescribed a nonselective beta-blocking agent is postural hypotension. Nonselective beta blockers work by blocking beta-1 receptors in the heart, which leads to a decrease in heart rate and blood pressure. This can cause a drop in blood pressure when the client changes positions from lying down to standing up, resulting in postural hypotension.