Assertion: A person undergoes fatigue very soon during exercies.
Reason : Muscle fibres undergo oxygen debt during exercies.

Options

A. If both assertion and reason are ture and reason is the corect explanation of assertion
B. If both assertion and reason are ture but reson is not the correct explanation of assertion
C. If assertion is true reason is false
D. If both assertion and reason are false

Explanation

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that a person undergoes fatigue very soon during exercise. This is a common observation during strenuous physical activity, where individuals often feel tired quickly.

2. **Understanding the Reason**: The reason provided is that muscle fibers undergo oxygen debt during exercise. Oxygen debt refers to the state where the muscles do not receive enough oxygen to meet their energy demands, leading to a shift in how energy is produced.

3. **Linking Assertion and Reason**: During intense exercise, muscles require more energy, which is typically produced through aerobic respiration. However, when oxygen supply is insufficient, muscles switch to anaerobic respiration, which leads to the production of lactic acid.

4. **Effects of Lactic Acid**: The accumulation of lactic acid in the muscles is a byproduct of anaerobic respiration. This buildup can lead to muscle fatigue, causing the person to feel tired more quickly during exercise.

5. **Evaluating the Assertion and Reason**:
- The assertion is correct: a person does experience fatigue quickly during exercise.
- The reason is also correct: muscle fibers do undergo oxygen debt during exercise.
- However, the reason provided does not fully explain the assertion. The fatigue is primarily due to lactic acid accumulation from anaerobic respiration, not solely due to oxygen debt.

6. **Conclusion**: Both the assertion and the reason are correct, but the reason is not the correct explanation for the assertion. Therefore, the answer is option B: Both assertion and reason are correct, but the reason is not the correct explanation for the assertion.