To solve the question "Which one of the following is a set of natural growth regulators?", we will analyze the options provided and identify which ones consist solely of natural growth regulators.
### Step-by-Step Solution:
1. **Understand the Concept of Plant Growth Regulators (PGRs)**:
- Plant growth regulators are chemicals that influence the growth and development of plants. They can be natural or synthetic.
2. **Identify the Types of Natural Growth Regulators**:
- The primary natural growth regulators include:
- Auxins (e.g., Indole Acetic Acid - IAA)
- Gibberellins
- Cytokinins (e.g., Zeatin)
- Ethylene
- Abscisic Acid (ABA)
3. **Examine the Options**:
- **Option 1**: NAA, IAA, IBA
- NAA (Naphthalene Acetic Acid) is a synthetic auxin. IAA (Indole Acetic Acid) and IBA (Indole Butyric Acid) are natural, but since NAA is synthetic, this option is incorrect.
- **Option 2**: 2,4-D, IBA, BAP
- 2,4-D (2,4-Dichlorophenoxyacetic Acid) is a synthetic auxin. IBA is natural, but since 2,4-D is synthetic, this option is incorrect.
- **Option 3**: 2,4-D, ABA, Ethylene
- Again, 2,4-D is synthetic. ABA (Abscisic Acid) and Ethylene are natural, but due to the presence of 2,4-D, this option is incorrect.
- **Option 4**: IAA, ABA, Zeatin
- IAA is a natural auxin, ABA is a natural growth regulator (stress hormone), and Zeatin is a natural cytokinin. All three are naturally occurring growth regulators.
4. **Conclusion**:
- The correct answer is **Option 4: IAA, ABA, Zeatin**, as all of these are natural growth regulators.
### Final Answer:
**Option 4: IAA, ABA, Zeatin** is the set of natural growth regulators.
