Assertion : `2^(nd)` period elements do not involve in excitation of electron.
Reason : `2^(nd)` period elements do not have vacant 2d-orbitals.

Options

A. If assertion is true but the reason is false
B. If assertion is false but reason is true
C. IF both assertion and reason are true and the reason is the correct explanation of assertion
D. If both assertion and reason are true but reason is not the correct explanation of assertion

Answer

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

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "2nd period elements do not involve in excitation of electron."
- This means that it claims these elements cannot promote electrons to higher energy levels.

2. **Evaluating the Assertion**:
- This statement is **false**.
- For example, in carbon (which is a 2nd period element), the electronic configuration is 1s² 2s² 2p².
- To form four covalent bonds (like in methane, CH₄), one of the 2s electrons must be excited to the 2p orbital, resulting in four half-filled orbitals that can overlap with hydrogen atoms to form bonds.

3. **Understanding the Reason**:
- The reason states that "2nd period elements do not have vacant 2d-orbitals."
- This implies that because there are no available d-orbitals in the 2nd period, these elements cannot undergo certain types of electronic transitions.

4. **Evaluating the Reason**:
- This statement is **true**.
- The 2d orbitals cannot exist because the principal quantum number (n=2) must be greater than the azimuthal quantum number (l=2). Therefore, 2d orbitals are not possible.

5. **Conclusion**:
- Since the assertion is false and the reason is true, the correct conclusion is that the assertion does not support the reason.
- The correct option is that the assertion is false, and the reason is true.

### Final Answer:
- The assertion is false, and the reason is true. Therefore, the correct option is option 2.