"Hair-on end" appearance is seen in -

Hair on end skull appearance is seen in the diploic space of skull,having the appearance of long veicle striations. These striations are due to alternating thickened trabeculae and radiolucent marrow hyperplasia seen in following conditions : Thalaseemia Major - Most common and characteristic feature sickle cell anemia Hereditary spherocytosis Severe iron deficiency anemia. Hence the single best answer would be Thalaseemia major