Assertion :Interspecific hybrids are usually sterile.
Reason : Interspecific hybrids receive chromosomes from two different species.

Options

A. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion, then mark (1)
B. If both Assertion and Reason are true ,but the Reason is not the correct explanation of the Assertion, then mark (2).
C. If Assertion is true, but Reason is false , then mark (3)
D. If both Assertion and Reason are false. , then mark (4)

Answer

### Step-by-Step Solution

1. **Understanding Interspecific Hybrids**:
- Interspecific hybrids are organisms that result from the mating of two different species. For example, a mule is a hybrid resulting from the mating of a male donkey and a female horse.

2. **Assertion Analysis**:
- The assertion states that "interspecific hybrids are usually sterile." This means that these hybrids cannot reproduce successfully. This is a well-documented phenomenon in biology.

3. **Reason Analysis**:
- The reason provided states that "interspecific hybrids receive chromosomes from two different species." This means that the genetic material (chromosomes) comes from two different species, which can lead to complications during reproduction.

4. **Linking Assertion and Reason**:
- The reason explains why the assertion is true. When two different species mate, their chromosomes may not pair correctly during meiosis (the process of cell division that produces gametes). This misalignment can lead to sterility in the hybrids.

5. **Conclusion**:
- Both the assertion and the reason are correct. The reason provided is a valid explanation for the assertion. Therefore, we conclude that interspecific hybrids are usually sterile because they receive chromosomes from two different species, leading to complications in reproduction.

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

---