Assertion : In oxidative phosphorylation , the electrons flow from NADH to `O_(2)`.
Reason :In photosynthesis , the electrons flow from `H_(2)O` to NADP.

Options

A. If both A and R are true and R is the correct explanation of A
B. If both A and R are true but R is not the correct explanation of A
C. If A is true but R is false
D. If both A and R are false

Answer

To analyze the assertion and reason provided in the question, we will break down the concepts of oxidative phosphorylation and photosynthesis step by step.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "In oxidative phosphorylation, the electrons flow from NADH to O2."
- In oxidative phosphorylation, which occurs in the mitochondria, NADH (a reduced form of NAD+) donates electrons to the electron transport chain. These electrons ultimately reduce oxygen (O2) to water (H2O). This process is crucial for ATP production.

2. **Evaluating the Assertion**:
- The flow of electrons from NADH to O2 is indeed correct. Therefore, the assertion is true.

3. **Understanding the Reason**:
- The reason states that "In photosynthesis, the electrons flow from H2O to NADP."
- In photosynthesis, particularly during the light-dependent reactions, water (H2O) is split (a process called photolysis) to release electrons. These electrons are then transferred to chlorophyll, which becomes excited by light energy and subsequently donates these electrons to NADP+, reducing it to NADPH.

4. **Evaluating the Reason**:
- The flow of electrons from water to NADP+ is also correct. Therefore, the reason is true.

5. **Conclusion**:
- Both the assertion and the reason are true statements. However, the reason does not serve as a correct explanation for the assertion because they pertain to different processes (oxidative phosphorylation vs. photosynthesis). Thus, while both statements are true, the relationship between them does not establish a cause-and-effect scenario.

### Final Answer:
- **Assertion**: True
- **Reason**: True
- **Explanation**: The reason is not the correct explanation of the assertion.