Choose the pair in which `IE_(1)` of first element is greater than `IE_(1)` of second element but in case of `IE_(2)` order is/are reversed

Options

A. `Mn gt Cr `
B. `Mn gt Fe `
C. `Zn gt Cu `
D. All of these

Answer

To solve the problem, we need to analyze the ionization enthalpies (IE) of the given pairs of elements. We are looking for a pair where the first ionization energy (IE1) of the first element is greater than that of the second element, but the second ionization energy (IE2) of the second element is greater than that of the first element.

### Step-by-Step Solution:

1. **Identify the Elements and Their Configurations**:
- We need to look at the electronic configurations of the elements in each pair to understand their ionization energies.
- For example, consider the pair Manganese (Mn) and Chromium (Cr):
- Mn: Atomic number 25, Configuration: [Ar] 3d5 4s2
- Cr: Atomic number 24, Configuration: [Ar] 3d5 4s1

2. **Analyze the First Ionization Energy (IE1)**:
- The first ionization energy is the energy required to remove the outermost electron.
- For Mn, removing an electron from 4s2 results in a configuration of 3d5 4s1.
- For Cr, removing an electron from 4s1 results in a configuration of 3d5 4s0.
- Since Cr has a half-filled 3d subshell, it is more stable, making it easier to remove an electron from Mn than from Cr.
- Therefore, **IE1(Mn) > IE1(Cr)**.

3. **Analyze the Second Ionization Energy (IE2)**:
- The second ionization energy is the energy required to remove a second electron after the first has been removed.
- After the first ionization:
- Mn becomes 3d5 4s1.
- Cr becomes 3d5.
- Removing an electron from Mn (3d5 4s1) results in a half-filled d subshell (3d5), which is relatively stable.
- Removing an electron from Cr (3d5) results in a configuration of 3d4, which is less stable.
- Thus, **IE2(Cr) > IE2(Mn)**.

4. **Conclusion**:
- We find that for the pair (Mn, Cr):
- **IE1(Mn) > IE1(Cr)** and **IE2(Cr) > IE2(Mn)**.
- This satisfies the condition given in the question.

5. **Check Other Pairs**:
- Repeat the analysis for other pairs (if provided) to ensure they do not meet the criteria.
- For example, analyze pairs like (Mn, Fe) and (Zn, Cu) similarly.

6. **Final Answer**:
- The pair that satisfies the condition is (Mn, Cr).