The term "auxin" is used for –

Options

A. IAA
B. NAA
C. 2, 4-D and 2, 4, 5-T
D. All

Answer

### Step-by-Step Solution:

1. **Definition of Auxin**: The term "auxin" refers to a class of plant hormones that play a crucial role in regulating plant growth and development. Auxins are involved in various processes such as cell elongation, root formation, and fruit development.

2. **Discovery of Auxin**: Auxin was first discovered and isolated from human urine. This historical context is important as it highlights the origins of auxin research.

3. **Types of Auxins**: There are two main types of auxins:
- **Natural Auxins**: These are produced naturally by plants. The most common natural auxin is Indole-3-Acetic Acid (IAA). Another example is Indole-3-Butyric Acid (IBA).
- **Synthetic Auxins**: These are artificially created compounds that mimic the action of natural auxins. Examples include 2,4-Dichlorophenoxyacetic acid (2,4-D) and 2,4,5-Trichlorophenoxyacetic acid (2,4,5-D).

4. **Conclusion**: The term "auxin" encompasses both natural and synthetic types of these plant hormones. Therefore, the correct answer to the question "The term 'auxin' is used for" would be option 4, which includes all types of auxins mentioned.