Step 1: Understanding the Problem:
Plant growth regulators (PGRs) control various developmental processes. Both Auxins and Ethylene have distinct agricultural applications regarding flowering in certain plants.
Step 2: Approach and Formula:
Map the specific agricultural applications (specifically "synchronising fruit set" along with initiating flowering in pineapples) to the correct plant growth regulator.
Step 3: Detailed Explanation:
While Auxins (like NAA and 2,4-D) are known to promote flowering in pineapples, the specific combined function of "initiating flowering" AND "synchronising fruit-set" is a hallmark function of Ethylene.
Ethylene is widely used in agriculture for this precise purpose, ensuring that all pineapple plants in a field flower and produce fruit at the same time, which is highly beneficial for harvesting.
Step 4: Final Answer:
The correct hormone is Ethylene.