Concept:Phosphorus is essential for root growth and reproductive development such as fruit and seed formation.Explanation:Phosphorus deficiency disrupts cell division and energy transfer in plants.This directly causes poor root development and inhibits fruit formation.Iron and chlorine deficiencies primarily cause chlorosis, or yellowing of leaves.Nitrogen deficiency mainly causes yellowing of older leaves, not inhibited root or fruit formation.Therefore, the deficiency symptoms described match phosphorus.Answer:D. phosphorus