Assertion : Fungi are heterotrophic.
Reason : They lack chlorophyll.

Options

A. If both assertion and reason 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

**Step-by-Step Solution:**

1. **Understanding the Assertion**: The assertion states that "Fungi are heterotrophic." This means that fungi cannot produce their own food and must obtain it from other sources.

2. **Understanding the Reason**: The reason given is "They lack chlorophyll." Chlorophyll is a pigment found in plants that is essential for photosynthesis, the process by which plants convert light energy into chemical energy (food).

3. **Linking Assertion and Reason**: Since fungi do not have chlorophyll, they cannot perform photosynthesis. This inability to synthesize their own food is what classifies them as heterotrophic organisms.

4. **Defining Heterotrophic Organisms**: Heterotrophic organisms are those that cannot produce their own food and rely on other organisms for nutrition. Fungi can obtain their nutrients in two main ways: as saprophytes (feeding on dead organic matter) or as parasites (feeding on living organisms).

5. **Conclusion**: Both the assertion and the reason are correct. The reason provided (lack of chlorophyll) correctly explains why fungi are classified as heterotrophic.

6. **Final Answer**: Therefore, the correct option is that both the assertion and reason are correct, and the reason is a correct explanation of the assertion.

---