Which of following elements is required in the synthesis of plant growth hormone such as auxin ?

Options

A. Mo
B. Cu
C. Zn
D. Mg

Answer

To solve the question regarding which element is required in the synthesis of plant growth hormones such as auxin, we will analyze each option provided.

### Step-by-Step Solution:

1. **Understand the Question**: The question asks which element is necessary for the synthesis of plant growth hormones, specifically auxins.

2. **Evaluate Option 1: Molybdenum**:
- Molybdenum is known to be a component of certain enzymes like nitrate reductase and nitrogenase.
- Its primary role is in nitrogen metabolism rather than in the synthesis of auxins.
- **Conclusion**: Molybdenum is NOT required for auxin synthesis.

3. **Evaluate Option 2: Copper**:
- Copper plays a role in photosynthesis and respiration in plants.
- While it is an essential micronutrient, it is not directly involved in the synthesis of auxins.
- **Conclusion**: Copper is NOT required for auxin synthesis.

4. **Evaluate Option 3: Zinc**:
- Zinc is known to be involved in the synthesis of plant hormones, including auxins.
- It acts as a cofactor for various enzymes that are crucial in the biosynthesis of these hormones.
- **Conclusion**: Zinc IS required for auxin synthesis.

5. **Evaluate Option 4: Magnesium**:
- Magnesium is important for activating certain enzyme systems and is a central component of chlorophyll.
- However, it does not play a direct role in the synthesis of auxins.
- **Conclusion**: Magnesium is NOT required for auxin synthesis.

6. **Final Conclusion**: Based on the evaluations, the correct answer to the question is **Zinc** (Option 3), as it is the element required in the synthesis of plant growth hormones like auxin.