If atomic number of an inert gas is Z then an element with which of the following atomic number will has highest I.E.

Options

A. `Z-2`
B. `Z-1`
C. `Z+1`
D. `Z+2`

Explanation

To determine which element has the highest ionization energy (I.E.) when given an inert gas with atomic number Z, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Inert Gas Configuration**:
- The inert gases (noble gases) have a complete outer shell configuration, which is generally represented as \( ns^2 np^6 \). For an inert gas with atomic number Z, its electronic configuration can be considered as \( [Xe] \) or similar, depending on the period.

2. **Consider the Atomic Numbers**:
- The question provides options based on atomic numbers relative to Z:
- \( Z - 2 \)
- \( Z - 1 \)
- \( Z + 1 \)
- \( Z + 2 \)

3. **Analyze Each Option**:
- **For \( Z - 2 \)**: This corresponds to an element that would have lost two electrons from the inert gas configuration, likely resulting in a group 16 element (\( ns^2 np^4 \)). This element will have a relatively lower I.E. due to the presence of more electrons and less effective nuclear charge felt by the outer electrons.

- **For \( Z - 1 \)**: This corresponds to an element that would have lost one electron, likely resulting in a group 17 element (halogens, \( ns^2 np^5 \)). Halogens have high I.E. because they are one electron short of a noble gas configuration, making it energetically favorable to gain an electron rather than lose one.

- **For \( Z + 1 \)**: This corresponds to a group 1 element (\( ns^1 \)). Group 1 elements have low I.E. because they have only one electron in their outer shell, which is easily removed.

- **For \( Z + 2 \)**: This corresponds to a group 2 element (\( ns^2 \)). While these elements have a higher I.E. than group 1, they still have lower I.E. compared to halogens.

4. **Determine the Highest I.E.**:
- Among these options, the group 17 element (from option \( Z - 1 \)) will have the highest ionization energy. This is because it is closer to achieving a noble gas configuration by gaining one electron rather than losing one, which requires significantly more energy.

### Conclusion:
The element with atomic number \( Z - 1 \) will have the highest ionization energy.