The best defined function of manganese is

Options

A. in the splitting of water to liberate oxygen during photosynthesis
B. in the synthesis of auxin.
C. activates enzymes in respiration and photosynthesis, and in the synthesis of DNA and RNA
D. it is associated with certain enzymes involved in redox reactions

Explanation

To answer the question about the best-defined function of manganese in plants, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Form of Manganese in Plants**:
- Manganese is absorbed by plants in the form of manganese ions (Mn²⁺). This is the first step in understanding its role in plant physiology.

2. **Understand the Role of Manganese in Photosynthesis**:
- One of the most critical functions of manganese is its involvement in the splitting of water molecules during photosynthesis. This process is essential for the liberation of oxygen, which is a byproduct of photosynthesis.

3. **Evaluate Other Functions Mentioned**:
- The transcript mentions other functions that are often confused with manganese's role:
- **Synthesis of Auxins**: This is primarily associated with other elements, particularly zinc.
- **Activation of Enzymes in Respiration and Photosynthesis**: This role is mainly attributed to magnesium, not manganese.
- **Involvement in Redox Reactions**: This function is primarily linked to iron.

4. **Conclude with the Best Defined Function**:
- Based on the information gathered, the best-defined function of manganese is its role in the splitting of water during photosynthesis, which is crucial for oxygen liberation.

### Final Answer:
The best defined function of manganese is its role in the splitting of water to liberate oxygen during photosynthesis.

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