Sonia went to the market along with her mother to buy fruits. She saw the fruit dealer putting small quantity of some powder wrapped in a paper in each wooden pack containing unripe mangoes. On enquiry, the fruit dealer told him that the powder is specific chemical which will help the mangoes to ripe early. Sonia was not convinced and he discussed the incidence with his class teacher the next day.
The substance that triggers the fall of mature leaves and fruits from plants is due to

Options

A. auxin
B. gibberellin
C. abscisic acid
D. cytokinin

Explanation

**Step-by-Step Solution:**

1. **Understanding the Context**: Sonia observed a fruit dealer using a powder to help mangoes ripen faster. This raises questions about the substances involved in plant growth and development.

2. **Identifying the Substances**: The question mentions several substances: oxygen, chivalrin, abscisic acid, and cytokinin. We need to determine which of these is responsible for triggering the fall of mature leaves and fruits.

3. **Researching Plant Hormones**:
- **Abscisic Acid**: This hormone is known to play a significant role in the process of leaf and fruit abscission (the dropping of leaves and fruits). It signals the plant to shed parts that are no longer needed.
- **Cytokinins**: These promote cell division and are generally associated with growth rather than abscission.
- **Gibberellins**: These are involved in stem elongation and seed germination, not in the dropping of leaves or fruits.
- **Oxygen**: While essential for respiration, it does not directly trigger leaf or fruit fall.

4. **Conclusion**: Based on the functions of these substances, abscisic acid is the correct answer as it is responsible for the abscission of leaves and fruits from plants.

5. **Final Answer**: The substance that triggers the fall of mature leaves and fruits from plants is **abscisic acid**.

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