In `C_(3)` cycle for the fixation of every `CO_(2)` molecule, the reduction and regeneration steps require :

Options

A. 3 ATP and 2 `NADPH_(2)`
B. 2 ATP and 2 `NADPH_(2)`
C. 2 ATP and 3 `NADPH_(2)`
D. 3 ATP and 3 `NADPH_(2)`

Answer

To answer the question regarding the requirements for the fixation of every CO₂ molecule in the C₃ cycle, let's break down the steps involved in the reduction and regeneration phases of the cycle.

### Step-by-Step Solution:

1. **Understanding the C₃ Cycle**: The C₃ cycle, also known as the Calvin cycle, is the process by which plants fix carbon dioxide (CO₂) into organic molecules. This cycle consists of three main phases: carbon fixation, reduction, and regeneration.

2. **Carbon Fixation**: In the first step, CO₂ is fixed by combining with ribulose bisphosphate (RuBP) to form 3-phosphoglyceric acid (3-PGA). This step does not require ATP or NADPH directly.

3. **Reduction Phase**: In the reduction phase, 3-PGA is converted into glyceraldehyde-3-phosphate (G3P). This conversion requires energy and reducing power:
- **ATP Requirement**: The reduction of 3-PGA to G3P requires 3 ATP molecules.
- **NADPH Requirement**: Additionally, this step requires 2 NADPH molecules, which provide the reducing power.

4. **Regeneration Phase**: In the regeneration phase, G3P is used to regenerate RuBP, allowing the cycle to continue:
- **ATP Requirement**: The regeneration of RuBP from G3P requires another 3 ATP molecules.

5. **Total Requirements**: For the fixation of one molecule of CO₂, the total requirements for the reduction and regeneration steps are:
- **ATP**: 3 (for reduction) + 3 (for regeneration) = 6 ATP
- **NADPH**: 2 (for reduction)

6. **Final Answer**: Therefore, for the fixation of every CO₂ molecule in the C₃ cycle, the total requirements are 6 ATP and 2 NADPH.

### Summary:
- For every CO₂ molecule fixed in the C₃ cycle, the reduction and regeneration steps require **6 ATP and 2 NADPH**.