Premature leaf fall is due to deficiency of
A. Potassium
B. Sodium
C. Phosphorus
D. Zinc

Hint: Two chemicals are responsible for the coloration of leaves. Anthocyanins produce red and purple pigments, while carotenoids produce orange and yellow pigments. During the summer, the carotenoids are present in the leaf, but they are obscured by the chlorophyll's green colour.

Complete answer:
Phosphorus is an essential macronutrient. Biosynthesis of nucleotides, nucleic acids, phospholipids and other biomolecules is crucial. Poor development and delayed seed germination are all symbols of poor blooms, dull green leaves, red anthocyanin spots, premature leaf fall, and preterm flower buds. In the form of phosphate ions, the plant absorbs phosphorus. It is all contained in cell membranes, ATP, nucleic acids, phospholipids, and some coenzymes. Its deficiency causes stunted growth, chlorosis, necrosis and premature leaf fall.

So, the correct answer is 'Phosphorus'.

Additional information:
Abscisic acid is a plant chemical discovered for its role in controlling abscission (the regular separation of plant parts, usually dead leaves and ready leafy foods). Abscisic acid is especially important for plants in responding to natural stresses such as dry season, soil saltiness, cold resistance, freezing resilience, heat pressure, and heavy metal particle resilience. It hastens the closure of stomata and the fall of senescent leaves.

Note:
As a result, Abscisic acid is the plant chemical responsible for the dropping of senescent leaves. The detachment or dropping of older leaves is known as leaf abscission. It appears at the petiole's foundation. During leaf fall, high abscisic acid synthesis is observed, along with a decrease in auxin concentration. It loosens the cell wall and causes cells to divide, resulting in leaf abscission.