Assertion :- Fossils are always remains of hard parts of life -forms found only in rocks.
Reason :- Organisms get buried in soil crust when they die .

Options

A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion.
B. If both Assertion & Reason are True but Reason is a not a correct explanation of the Assertion.
C. If Assertion is True but the Reason is False.
D. If both Assertion & Reason are false.

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that "Fossils are always remains of hard parts of life-forms found only in rocks." This means that fossils primarily consist of the hard structures of organisms, such as bones, teeth, and shells, which are preserved in sedimentary rock formations.

2. **Understanding the Reason**: The reason states that "Organisms get buried in soil crust when they die." This implies that when organisms die, they can be covered by sediment, which eventually leads to fossilization.

3. **Analyzing the Assertion**: Fossils are indeed most commonly found in sedimentary rocks, as these rocks form from the accumulation of sediments over time. The hard parts of organisms are more likely to be preserved because they resist decay better than soft tissues.

4. **Analyzing the Reason**: When organisms die, they can be buried by sediment, which protects them from decomposition and allows fossilization to occur. This process is essential for the formation of fossils.

5. **Conclusion**: Both the assertion and the reason are true. Fossils are primarily the remains of hard parts of life forms found in rocks, and the process of burial in sediments is crucial for fossil formation.

6. **Final Answer**: Since both the assertion and the reason are true and the reason correctly explains the assertion, the correct option is that both the assertion and reason are true.