ANS:C - P₂O₅

Phosphorus pentoxide (P2O5) is a chemical compound composed of two phosphorus atoms and five oxygen atoms. It is an anhydride of phosphoric acid (H3PO4). In the context of fertilizers, P2O5 is used to measure the phosphorus content. When applied to soil, phosphorus in the form of P2O5 is gradually converted into phosphate ions, which plants can absorb and utilize for various metabolic processes, particularly in promoting root development, flower and fruit formation, and overall plant growth.