A: For every `CO_(2)` molecule entering `C_(3)` cycle , three molecules of ATP and two NADPH are required .
R: Cyclic photophosphorylation takes place to meet the difference in number of ATP.

Options

A. If both Assertion % Reson ar true and the reason is the correct explanation of the asserition the mark (1)
B. If both Assertion % Reason are true but the reason, is not the correct explanation of the assertion ,then mark (2)
C. If Assetion is true statement but Reason is false , The mark (3)
D. If both Assertion and Reason are false statements, the mark (4)

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that for every molecule of CO₂ entering the C3 cycle (Calvin cycle), three molecules of ATP and two molecules of NADPH are required. This is true because the Calvin cycle involves a series of reactions where ATP and NADPH are used to convert CO₂ into glucose.

2. **Analyzing the Calvin Cycle**: In the Calvin cycle:
- **Carboxylation**: CO₂ combines with ribulose bisphosphate (RuBP) to form a 3-carbon compound (3-phosphoglycerate).
- **Reduction Phase**: This compound is then reduced using ATP and NADPH to form glyceraldehyde-3-phosphate (G3P).
- **Regeneration Phase**: Some G3P molecules are used to regenerate RuBP, which requires additional ATP.

3. **Calculating ATP and NADPH Requirements**: For every turn of the Calvin cycle:
- 3 ATP and 2 NADPH are consumed per CO₂ molecule.
- To synthesize one glucose molecule, the cycle must turn 6 times, requiring a total of 18 ATP and 12 NADPH.

4. **Understanding the Reason**: The reason states that cyclic photophosphorylation occurs to meet the difference in the number of ATP required. This is also true because the Calvin cycle requires more ATP than NADPH.

5. **Role of Cyclic Photophosphorylation**:
- Cyclic photophosphorylation occurs in the thylakoid membranes and involves only Photosystem I (PSI).
- It generates additional ATP without producing NADPH, which helps to balance the ATP/NADPH ratio needed for the Calvin cycle.

6. **Conclusion**: Both the assertion and the reason are correct. The reason correctly explains why cyclic photophosphorylation is necessary to provide the additional ATP required for the Calvin cycle.

### Final Answer:
Both the assertion (A) and the reason (R) are true, and R is the correct explanation of A.

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