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

Answer

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

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

- **Understanding Oscillatory Motion**: Oscillatory motion refers to any motion that repeats itself in a regular cycle. This includes motions like a pendulum swinging back and forth.
- **Understanding Periodic Motion**: Periodic motion is a broader category that includes any motion that repeats after a fixed interval of time.

**Conclusion for Assertion**: The first part of the assertion is true; all oscillatory motions are indeed periodic because they repeat in cycles. However, the second part is false; not all periodic motions are oscillatory. For example, a car driving in a circular path is periodic but not oscillatory.

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

- **Understanding Simple Pendulum**: A simple pendulum exhibits oscillatory motion as it swings back and forth about a mean position. It is a classic example of simple harmonic motion, which is a type of oscillatory motion.

**Conclusion for Reason**: This statement is true; a simple pendulum is indeed an example of oscillatory motion.

### Final Conclusion
- The assertion is **false** because it incorrectly claims that all periodic motions are oscillatory.
- The reason is **true** because it accurately describes the simple pendulum as an example of oscillatory motion.

### Final Answer
- Assertion: False
- Reason: True

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