Mg and Fe are needed for plants in the

Options

A. (a) energy transfer
B. (b) synthesis of chlorophyll pigment in the leaves
C. (c) stomatal opening
D. (d) translocation of carbohydrates .

Answer

### Step-by-Step Solution:

1. **Identify the Nutrients**: The question mentions magnesium (Mg) and iron (Fe) as essential nutrients for plants.

2. **Classify the Nutrients**:
- Magnesium is classified as a macronutrient, meaning it is required in larger quantities by plants.
- Iron is classified as a micronutrient, which means it is needed in trace amounts.

3. **Role of Magnesium in Plants**:
- Magnesium is essential for normal growth and is required in all growing tissues, including leaves, stems, roots, and shoots.
- It is a component of magnesium pectate in cell walls, contributing to the structural integrity and shape of plant parts.
- Magnesium forms the central ring structure of chlorophyll, which is crucial for photosynthesis and helps in the synthesis and function of chlorophyll.

4. **Role of Iron in Plants**:
- Iron acts as an activator for enzymes, such as cytochrome, which are involved in the electron transport chain (ETC) and energy transfer.
- It also plays a role in the synthesis and function of chlorophyll, similar to magnesium.

5. **Deficiency Symptoms**:
- Both magnesium and iron deficiencies lead to chlorosis, which is characterized by yellowing of leaves due to a lack of chlorophyll, and can also result in stunted growth.

6. **Analyze the Options**:
- Option A: Energy transfer - This is true for iron but not for magnesium, so it is not the correct answer.
- Option B: Synthesis of chlorophyll pigment in the leaves - Both magnesium and iron are involved in chlorophyll synthesis, making this a strong candidate for the correct answer.
- Option C: Stomatal opening - This is primarily regulated by potassium and hydrogen ions, so it is incorrect.
- Option D: Translocation of carbohydrates - This is mediated by boron, making it incorrect as well.

7. **Conclusion**: Based on the analysis, the correct answer is **Option B**: Synthesis of chlorophyll pigment in the leaves.