Assertion :- Underground stem helps in perennation.
Reason :- Underground stem can overcome adverse environmental conditions.

Options

A. If both Assertion & Reason are True & Reason is a correct explanation of the Assertion.
B. If both Assertion & Reason are True & the Reason is 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 "Underground stem helps in perennation." We need to clarify what perennation means. Perennation refers to the ability of a plant to survive for long periods, especially through adverse environmental conditions.

**Hint**: Recall the definition of perennation and its significance for plant survival.

2. **Identifying the Role of Underground Stems**: Underground stems are modified structures that remain beneath the soil. They serve multiple functions, including storage of nutrients and food, as well as the propagation of new plants (clones).

**Hint**: Think about the adaptations of plants that allow them to survive in different environments.

3. **Examples of Underground Stems**: An example of an underground stem is the rhizome found in ginger. These structures allow the plant to store nutrients and survive through unfavorable seasons.

**Hint**: Consider how certain plants adapt to seasonal changes through their structures.

4. **Evaluating the Reason**: The reason states that "Underground stem can overcome adverse environmental conditions." This is indeed correct, as the underground stem stores nutrients that help the plant endure tough conditions, such as drought or extreme temperatures.

**Hint**: Reflect on how storage in plants contributes to their survival during harsh conditions.

5. **Conclusion**: Both the assertion and the reason are true. The reason correctly explains why the assertion is valid, as the underground stem's ability to store nutrients aids in the plant's survival over time.

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