Deficiency of which of the following elements is responsible for premature falling of leaves?

Phosphorus deficiency causes premature leaf fall because phosphorus is essential for energy transfer (ATP) and root development. When deficient, older leaves turn dark green or purplish, then yellow and fall off early as the plant mobilizes phosphorus from older tissues to new growth. Zinc, manganese, and boron deficiencies cause different symptoms like interveinal chlorosis, stunting, or cork formation.