The pH of lemon juice is in the 2.0 range, making it very effective against browning. Hence Ascorbic acid prevents over-ripening of banana and browning of cut fruits. So, the correct answer is 'Ascorbic acid'.

Introduction
The prevention of over-ripening of bananas and the browning of cut fruits is crucial in post-harvest handling and storage. Among the available options, the most effective agent is ascorbic acid.
Role of Ascorbic Acid
- Ascorbic acid, commonly known as Vitamin C, is a powerful antioxidant that plays a significant role in fruit preservation.
- It prevents enzymatic browning, which occurs when cut fruits are exposed to oxygen, leading to discoloration.
Mechanism of Action
- Ascorbic acid reduces the activity of polyphenol oxidase, the enzyme responsible for browning in fruits.
- By maintaining the fruit's visual appeal, ascorbic acid helps in retaining the quality and marketability of cut fruits.
Impact on Bananas
- In bananas, ascorbic acid helps to delay the ripening process by inhibiting ethylene production, a hormone that accelerates ripening.
- This action can extend the shelf life of bananas, making them more appealing for consumers.
Comparison with Other Options
- Gibberellic Acid: Primarily promotes growth and elongation in plants, not effective in preventing ripening.
- Indole-3 Acetic Acid: A type of auxin that influences growth but does not prevent browning or ripening.
- Abscisic Acid: Involved in stress responses and seed dormancy, it does not directly inhibit ripening or browning.
Conclusion
In conclusion, ascorbic acid is the most effective agent to prevent over-ripening of bananas and browning of cut fruits, ensuring better preservation and quality in post-harvest management.