Final answer:
The best response by the nurse would be to explain that the change in stool color is an expected side effect of the medication and is not a cause for concern.
Step-by-step explanation:
The best response by the nurse would be: "This is an expected side effect of ferrous sulfate (Feosol); it is okay."
Feosol is an iron supplement commonly used to treat iron deficiency anemia. One of the side effects of taking ferrous sulfate is dark or black stools. This is because iron can cause the stool to change color.
It is important for the nurse to reassure the client that this is a normal and expected side effect of the medication, as it can help alleviate the client's concerns and anxieties.