In each of the following questions a Statement of Assertion (A ) is given followed by a corresponding statement of Reason (R ) Just below it . Of the statement mark the correct answer as
Assertion . When the atoms of first transition series ionize the 4s- orbital electrons are ionized before the 3d- orbital electrons .
Reason . The energy of 3d- orbital electron is lower than that of 4s-orbital electronic .

Explanation

To analyze the given Assertion (A) and Reason (R), we can break down the statements step by step.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states: "When the atoms of the first transition series ionize, the 4s-orbital electrons are ionized before the 3d-orbital electrons."
- This means that during ionization, the electrons from the 4s orbital are removed before those from the 3d orbital.

2. **Understanding the Reason (R)**:
- The reason states: "The energy of 3d-orbital electron is lower than that of 4s-orbital electron."
- This implies that the 3d electrons have a lower energy level compared to the 4s electrons.

3. **Analyzing the Assertion**:
- In transition metals, the 4s orbital is filled before the 3d orbital. However, when it comes to ionization, the 4s electrons are removed first because they are considered to be in the valence shell.
- The assertion is **true** because the outermost electrons (4s) are removed before the inner electrons (3d).

4. **Analyzing the Reason**:
- The reason provided is incorrect. Although the 3d electrons are lower in energy when they are filled, during ionization, the 4s electrons are at a higher principal quantum number (n=4) compared to 3d (n=3).
- Therefore, the reason is **false** because it incorrectly states the energy relationship between the 4s and 3d orbitals.

5. **Conclusion**:
- Since the assertion is true and the reason is false, the correct answer is that the Assertion is true, and the Reason is false.

### Final Answer:
- The correct answer is: Assertion is true, Reason is false.