Answer: C
D50.9 is the correct code for this case because it codes for iron deficiency anemia that is unspecified. As the etiology is unknown, therefore the main factor for the anemia cannot be mentioned here.
Option A is not correct because D50.0 is used to code for iron deficiency anemia secondary to blood loss.
Option B is not correct because D50.8 is used to code for other iron deficiency anemias.
Option D is not correct because D50.1 is used to code for Sideropenic dysphagia which is not the diagnosis here.