Assertion: The motion of the earth around the sun is perriodic but not oscillatory.
Reason: Oscillatory motion is necessarily periodic but periodic motion is not necessarily oscillatory.

Options

A. If both assertion and reson 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 assertion and reason question, we need to analyze both statements carefully.

### Step 1: Analyze the Assertion
The assertion states that "The motion of the earth around the sun is periodic but not oscillatory."

- **Periodic Motion**: A motion is termed periodic if it repeats after a regular interval of time. The Earth's orbit around the sun takes approximately one year to complete, which means it repeats this motion every year. Therefore, this part of the assertion is correct.

- **Oscillatory Motion**: Oscillatory motion refers to motion that occurs back and forth around a central point or equilibrium position. Examples include a pendulum swinging or a mass on a spring. The Earth's motion around the sun does not fit this definition as it does not oscillate back and forth around a central point; rather, it follows a circular or elliptical path.

Thus, the assertion is **true**.

### Step 2: Analyze the Reason
The reason states that "Oscillatory motion is necessarily periodic but periodic motion is not necessarily oscillatory."

- This statement is also true. Every oscillatory motion is periodic because it repeats itself after a specific time interval. However, not all periodic motions are oscillatory. For example, the motion of the Earth around the sun is periodic but not oscillatory, as previously discussed.

### Step 3: Conclusion
Both the assertion and the reason are true, but the reason does not correctly explain the assertion. The assertion is about the nature of the Earth's motion, while the reason discusses the relationship between oscillatory and periodic motions in general.

### Final Answer
Both the assertion and reason are true, but the reason is not the correct explanation of the assertion. Therefore, the correct option is **B**.

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