To solve the question regarding the electron gain enthalpy of Oxygen, Sulphur, Selenium, and Tellurium, we will analyze the trends in electron gain enthalpy across the group in the periodic table.
### Step-by-Step Solution:
1. **Understanding Electron Gain Enthalpy**:
- Electron gain enthalpy is the amount of energy released when an electron is added to a neutral atom in the gaseous state. It is typically expressed in kJ/mol.
2. **Periodic Trend**:
- As we move down a group in the periodic table, the electron gain enthalpy generally decreases. This is due to the increase in atomic size and the corresponding decrease in the effective nuclear charge experienced by the added electron.
3. **Comparing Elements**:
- **Oxygen (O)**: Being at the top of the group, it has a smaller atomic size and higher effective nuclear charge, which leads to a relatively higher (more negative) electron gain enthalpy. However, due to inter-electronic repulsion in the small 2p orbital, the electron gain enthalpy is less favorable compared to the heavier elements.
- **Sulfur (S)**: As we move down to sulfur, the atomic size increases, and the electron gain enthalpy becomes less negative compared to oxygen but more negative than selenium and tellurium.
- **Selenium (Se)**: Further down the group, selenium has an even larger atomic size, leading to a further decrease in the electron gain enthalpy.
- **Tellurium (Te)**: Tellurium, being the heaviest, has the least negative electron gain enthalpy due to the largest atomic size and the weakest attraction of the nucleus on the added electron.
4. **Order of Electron Gain Enthalpy**:
- Based on the above analysis, we can summarize the order of electron gain enthalpy from most negative (highest energy release) to least negative (lowest energy release) as follows:
- Sulfur > Selenium > Tellurium > Oxygen
5. **Final Values**:
- The approximate values for the electron gain enthalpy (in kJ/mol) are:
- Oxygen: -141 kJ/mol
- Sulfur: -200 kJ/mol
- Selenium: -196 kJ/mol
- Tellurium: -190 kJ/mol
### Conclusion:
The electron gain enthalpy of Oxygen, Sulfur, Selenium, and Tellurium respectively are approximately:
- Oxygen: -141 kJ/mol
- Sulfur: -200 kJ/mol
- Selenium: -196 kJ/mol
- Tellurium: -190 kJ/mol
