Assertion : All oscillatory motions are necessarily periodic motion but all periodic motion are not oscillatory.
Reason : Simple pendulum is an example of oscillatory motion.

Options

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

Answer

To solve the question, we need to analyze the assertion and the reason provided.

### Step 1: Understand the Assertion
The assertion states: "All oscillatory motions are necessarily periodic motion but all periodic motion are not oscillatory."

- **Explanation**:
- Oscillatory motion refers to motion that repeats itself over time around a central point (equilibrium position). Examples include the motion of a pendulum or a mass on a spring.
- Periodic motion refers to any motion that repeats after a fixed interval of time, regardless of whether it oscillates around a central point. For instance, the rotation of the Earth is periodic but not oscillatory.

### Step 2: Understand the Reason
The reason states: "Simple pendulum is an example of oscillatory motion."

- **Explanation**:
- A simple pendulum swings back and forth around its central position (the lowest point of its swing). This motion is periodic because it repeats after a fixed time interval (the time period of the pendulum). Thus, the simple pendulum is indeed an example of oscillatory motion.

### Step 3: Analyze the Relationship Between Assertion and Reason
- The assertion is correct because all oscillatory motions are periodic by definition. However, not all periodic motions are oscillatory, as demonstrated by the example of the Earth's rotation.
- The reason is also correct because a simple pendulum is indeed an example of oscillatory motion. However, it does not provide a sufficient explanation for the assertion.

### Conclusion
- Both the assertion and reason are correct, but the reason does not adequately explain the assertion. Therefore, the correct answer is that the assertion is true, the reason is true, but the reason is not the correct explanation for the assertion.

### Final Answer
- The assertion is true, the reason is true, but the reason is not the correct explanation for the assertion.

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