Assertion : There are 72-75 heart beats per minute on an average when a person is performing normal work
Reason : One heart beat is completed in 0.8 second.

Options

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

Explanation

To solve the question, we will analyze both the assertion and the reason provided.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that there are 72-75 heartbeats per minute on average when a person is performing normal work.
- This is a well-known fact; the average resting heart rate for adults typically ranges from 60 to 100 beats per minute, and during normal activities, it can be around 72-75 beats per minute.

2. **Understanding the Reason**:
- The reason states that one heartbeat is completed in 0.8 seconds.
- To verify this, we can calculate the number of beats per minute based on the duration of one heartbeat.
- If one heartbeat takes 0.8 seconds, then in one minute (60 seconds), the number of heartbeats can be calculated as:
\[ \text{Number of beats} = \frac{60 \text{ seconds}}{0.8 \text{ seconds/beat}} = 75 \text{ beats} \]
- This calculation confirms that if one heartbeat is indeed 0.8 seconds, then the heart would beat approximately 75 times in one minute.

3. **Conclusion**:
- Both the assertion and the reason are true.
- The reason correctly explains the assertion because the calculation of heartbeats per minute based on the duration of one heartbeat (0.8 seconds) aligns with the assertion of 72-75 beats per minute.

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