The best growth regulator for controlling fruit drop is

✅Explanation:
NAA is a synthetic auxin that is widely used as a plant growth regulator to control pre-harvest fruit drop in many fruit crops like mango, citrus, and guava. It helps in reducing fruit drop by promoting cell division and strengthening the attachment of fruits to the plant.
NAA is known for its ability to promote root formation in cuttings, enhance fruit setting and development, and prevent premature fruit drop.
It is commonly used as a foliar spray or applied directly to the plant’s tissues.
NAA works by stimulating cell elongation and differentiation, influencing various physiological processes in plants.
However, improper dosage or application of NAA can lead to adverse effects such as leaf burning or abnormal growth.

📌Other Options Explanations:
(a) IAA (Indole Acetic Acid):IAA is a natural auxin and plays a role in plant growth and development. IAA is more involved in promoting root growth and other developmental processes.
(c) MH (Maleic Hydrazide):MH is primarily used as a growth retardant to inhibit sprouting in storage crops like onions and potatoes.
(d) GA3 (Gibberellic Acid):GA3 is involved in promoting fruit enlargement and flowering. In fact, it may sometimes enhance fruit drop due to its influence on growth dynamics.

• Related Terminology:
Pre-harvest Fruit Drop: The natural phenomenon where fruits detach from the plant before maturity, leading to yield loss.
Abscission Layer: A specialized zone of cells at the base of the fruit stalk that weakens and facilitates fruit detachment when mature.