Ethylene is used to initiate flowering and for synchorinising fruit set in pineapples.

Answer

### Step-by-Step Solution:

1. **Understanding Ethylene**: Ethylene is a gaseous plant hormone that plays a crucial role in various physiological processes in plants, including flowering and fruit development.

2. **Role in Flowering**: Ethylene is known to initiate flowering in certain plants, including pineapples. It helps in the transition from vegetative growth to flowering, making it essential for the reproductive phase of the plant.

3. **Synchronizing Fruit Set**: In addition to initiating flowering, ethylene also helps in synchronizing fruit set. This means that it can cause multiple flowers to bloom and set fruit at the same time, which is particularly beneficial for commercial cultivation.

4. **Mechanism of Action**: Ethylene acts by promoting various biochemical processes that lead to flowering and fruit development. It is involved in the ripening of fruits, promoting abscission (the shedding of leaves and flowers), and influencing senescence (aging) in plants.

5. **Application in Agriculture**: Ethylene is often applied in agriculture in the form of ethephon, a compound that releases ethylene slowly when dissolved in water. This method allows for controlled application to enhance flowering and fruit set in crops like pineapples.

6. **Conclusion**: The statement that ethylene is used to initiate flowering and synchronize fruit set in pineapples is correct. Ethylene's role as a phytohormone is well-documented in plant physiology.