Final answer:
The child's hemoglobin level increasing is a sign of adherence to ferrous sulfate therapy in iron deficiency anemia.
Step-by-step explanation:
To determine adherence to ferrous sulfate therapy in a child with iron deficiency anemia, several data points can be considered. The child's hemoglobin level increasing (option a) would indicate a positive response to the therapy. This is because hemoglobin is the protein responsible for carrying oxygen in red blood cells, and iron is a crucial component of hemoglobin.
On the other hand, options b, c, and d are not direct indicators of adherence to the therapy. The child's stool turning black (option b) is a side effect of iron supplementation, while the child's parents reporting medication adherence (option c) is subjective and may not accurately reflect actual adherence. Lastly, the child's blood iron level increasing (option d) is expected if the therapy is effective, but it does not confirm adherence specifically.