Assertion : Parallax method cannot be used for measuring distance of stars morer then 100 light year away.
Reason : Because parallax angle reduces so much that it cannot be measured accurately.

Options

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

Explanation

To solve the assertion and reason question regarding the parallax method for measuring distances to stars, we can break it down into a step-by-step analysis.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that the parallax method cannot be used for measuring the distance of stars more than 100 light years away.
- The parallax method relies on measuring the angle of parallax (θ) to determine the distance (D) to a star.

**Hint**: Recall that parallax is the apparent shift in position of an object when viewed from different perspectives.

2. **Understanding the Reason**:
- The reason given is that the parallax angle reduces so much for distant stars that it cannot be measured accurately.
- As the distance to the star increases, the angle θ decreases, making it harder to measure.

**Hint**: Think about how small angles can be difficult to measure accurately with standard instruments.

3. **Mathematical Relationship**:
- The relationship between distance (D) and parallax angle (θ) can be expressed as:
\[ D = \frac{L}{\theta} \]
where L is the baseline length (the distance between two observation points).
- As D increases, θ decreases, indicating an inverse relationship.

**Hint**: Remember that as the distance increases, the angle approaches zero, making it challenging to distinguish.

4. **Limit of Parallax Measurement**:
- There is a practical limit to how far we can measure using the parallax method. For distances greater than 100 light years, the parallax angle becomes too small to measure accurately.
- Therefore, the assertion that the parallax method cannot be used for stars more than 100 light years away is correct.

**Hint**: Consider the limits of measurement tools and how they affect our ability to gather data.

5. **Conclusion**:
- Both the assertion and the reason are true. The reason correctly explains why the assertion holds true: as the distance increases, the parallax angle decreases to a point where it is no longer measurable.

**Hint**: Reflect on how scientific methods often have limitations based on the tools and techniques available.

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