Final answer:
Administering ACE inhibitors to a client with essential hypertension helps prevent vasoconstriction and sodium and water retention, leading to relaxed blood vessels and lower blood pressure.
Step-by-step explanation:
The most appropriate rationale for administering an ACE inhibitor to a client diagnosed with essential hypertension is that ACE inhibitors prevent vasoconstriction and sodium and water retention. By inhibiting the action of the angiotensin converting enzyme (ACE), these medications reduce the formation of angiotensin II, a potent vasoconstrictor. This allows blood vessels to relax and widen, resulting in decreased resistance to blood flow and lower blood pressure.