Assertion : We cannot hear the sound produced by a vibrating pendulum.
Reason : The frequency of the pendulum is very less.

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 assertion is false but reason is true.

Explanation

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

### Step 1: Understand the Assertion
The assertion states: "We cannot hear the sound produced by a vibrating pendulum."
- This implies that the sound produced by a vibrating pendulum is not audible to the human ear.

### Step 2: Understand the Reason
The reason states: "The frequency of the pendulum is very less."
- This suggests that the frequency of the sound produced by the pendulum is below a certain threshold.

### Step 3: Determine the Threshold Frequency for Hearing
- The human ear can typically hear sounds in the frequency range of approximately 20 Hz to 20,000 Hz (20 kHz).
- Sounds with frequencies below 20 Hz are considered infrasonic and are not audible to humans.

### Step 4: Analyze the Frequency of the Pendulum
- The frequency of a vibrating pendulum is generally very low, often less than 20 Hz.
- Since the frequency of the pendulum is less than 20 Hz, it falls outside the audible range for humans.

### Step 5: Conclusion
- Since the frequency of the pendulum is indeed very low (less than 20 Hz), it confirms that we cannot hear the sound produced by it.
- Therefore, both the assertion and the reason are true, and the reason correctly explains the assertion.

### Final Answer
Both the assertion and the reason are true, and the reason is the correct explanation of the assertion. Thus, the answer is option 1.

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