A : `CaC_2` is interstitial carbide
R : Calcium ions are present in the Interstices .

Options

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

Answer

To solve the question, we need to analyze the assertion and reason provided:

**Assertion (A)**: `CaC_2` is an interstitial carbide.
**Reason (R)**: Calcium ions are present in the interstices.

### Step-by-Step Solution:

1. **Understanding Carbides**:
- Carbides are compounds formed between carbon and a metal. They can be classified into different types based on their structure and bonding characteristics.

**Hint**: Remember that carbides consist of carbon combined with metals.

2. **Definition of Interstitial Carbides**:
- Interstitial carbides are typically formed with transition metals. In these compounds, small carbon atoms occupy the interstitial sites within the metal lattice. The transition metals provide a host lattice structure.

**Hint**: Focus on the role of transition metals in forming interstitial carbides.

3. **Identifying the Metal in `CaC_2`**:
- Calcium (Ca) is an alkaline earth metal, not a transition metal. Therefore, `CaC_2` does not fit the criteria for being an interstitial carbide since it lacks the necessary transition metal host lattice.

**Hint**: Check the periodic table to distinguish between transition metals and other metals.

4. **Evaluating the Assertion**:
- Since `CaC_2` is made from calcium, which is not a transition metal, the assertion that `CaC_2` is an interstitial carbide is incorrect.

**Hint**: Recall the characteristics of interstitial carbides and the types of metals involved.

5. **Evaluating the Reason**:
- The reason states that calcium ions are present in the interstices. However, in the structure of `CaC_2`, it is the carbon atoms that occupy the interstitial sites, not calcium ions. Thus, this statement is also incorrect.

**Hint**: Consider what occupies interstitial sites in different types of carbides.

6. **Conclusion**:
- Both the assertion and the reason are false. Therefore, the correct answer is that both statements are incorrect.

### Final Answer:
Both the assertion (A) and reason (R) are false.

**Correct Option**: 4 (Both statements are false)