Which of the following mineral ion is used in the activation of enzymes responsible for respiration and photosynthesis?

Options

A. `Zn^(2+)`
B. `Mg^2`
C. `Na^(2+)`
D. `Ca^(2+)`

Answer

To solve the question regarding which mineral ion is used in the activation of enzymes responsible for respiration and photosynthesis, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Options**: The question provides four mineral ions: Zinc, Magnesium, Sodium, and Calcium.

2. **Understand the Role of Each Ion**:
- **Zinc**: This is a micronutrient that plays a role in various enzyme functions but is not primarily associated with respiration and photosynthesis.
- **Magnesium**: This is a macronutrient essential for plants. It is a key component of chlorophyll and is crucial for photosynthesis. Additionally, magnesium activates enzymes involved in respiration.
- **Sodium**: This is generally not essential for plant growth and is not directly involved in respiration or photosynthesis.
- **Calcium**: This is important for cell wall structure and signaling but does not directly activate enzymes for respiration and photosynthesis.

3. **Focus on Magnesium**: Since magnesium is known to be involved in the activation of enzymes that facilitate both respiration and photosynthesis, it stands out among the options.

4. **Conclusion**: Based on the analysis, the mineral ion that activates the enzymes responsible for respiration and photosynthesis is **Magnesium**.

### Final Answer:
**Magnesium**