For electron gain enthalpies of the elements denoted as `Delta_(eg)H`, the incorrect option is :

Options

A. `Delta_(eg)H(Cl) lt Delta_(eg)H(F)`
B. `Delta_(eg)H(I) lt Delta_(eg)H(At)`
C. `Delta_(eg)H(Te) lt Delta_(eg)H(Po)`
D. `Delta_(eg)H(Se) lt Delta_(eg)H(S)`

Answer

To solve the question regarding the incorrect option for the electron gain enthalpies of the elements, we will analyze the trends in electron gain enthalpy across periods and down groups in the periodic table.

### Step-by-Step Solution:

1. **Understanding Electron Gain Enthalpy**:
- Electron gain enthalpy (ΔegH) is the energy change when an electron is added to a neutral atom in the gas phase. It is usually expressed in kJ/mol.
- A more negative value indicates a greater tendency to gain an electron, while a less negative (or more positive) value indicates a lesser tendency.

2. **Analyzing Fluorine and Chlorine**:
- Fluorine (F) has a smaller atomic size compared to Chlorine (Cl).
- The small size of Fluorine leads to increased electron-electron repulsion when an additional electron is added, making it less favorable for Fluorine to gain an electron compared to Chlorine.
- Therefore, the electron gain enthalpy of Chlorine is more negative than that of Fluorine.

3. **Comparing Iodine and Astatine**:
- As we move down the group from Iodine (I) to Astatine (At), the atomic size increases.
- With an increase in size, the ability to attract an additional electron decreases due to increased shielding and distance from the nucleus.
- Hence, Iodine will have a more negative electron gain enthalpy compared to Astatine.

4. **Examining Tellurium and Polonium**:
- Similar to the halogens, as we move down the group from Tellurium (Te) to Polonium (Po), the electron gain enthalpy decreases.
- Therefore, Tellurium will have a more negative electron gain enthalpy than Polonium.

5. **Evaluating Sulfur and Selenium**:
- Sulfur (S) and Selenium (Se) are in the same group.
- As we move down the group, the electron gain enthalpy generally becomes less negative.
- Thus, Selenium will have a less negative electron gain enthalpy compared to Sulfur.

6. **Identifying the Incorrect Option**:
- Based on the above analysis, the order of electron gain enthalpy should be:
- Cl < F (Fluorine is less negative than Chlorine)
- I < At (Astatine is less negative than Iodine)
- Te < Po (Polonium is less negative than Tellurium)
- S < Se (Selenium is less negative than Sulfur)
- The incorrect statement would be regarding the comparison of Sulfur and Selenium, where it is incorrectly stated that Selenium has a more negative electron gain enthalpy than Sulfur.

### Conclusion:
The incorrect option regarding the electron gain enthalpies is related to the comparison of Sulfur and Selenium.