Final answer:
The correct response is 18 mg per day.
Step-by-step explanation:
The correct response from the nurse is D. 18 mg per day. According to the information provided, females between 11 and 50 years of age, as well as during pregnancy or lactation, require 18 mg of iron per day. Pregnancy increases the demand for iron due to the growth and development of the fetus, and the increased blood volume. Therefore, it is important for the primigravida patient to ensure she is getting the recommended amount of iron during her pregnancy.