Final answer:
The client should take the iron supplement on an empty stomach to ensure optimal absorption.
Step-by-step explanation:
The correct statement by the client that indicates an understanding of the teaching is option (b) "I'll take the iron supplement on an empty stomach."
Iron absorption is enhanced when taken on an empty stomach. This is because certain foods and beverages, such as milk, coffee, and meals high in fiber, can inhibit iron absorption. Taking the iron supplement on an empty stomach ensures optimal absorption of the iron.