In which of the following energy released will be largest on gaining an electron?

Options

A. Oxygen
B. Sulphur
C. Selenium
D. Tellurium

Answer

To determine which element releases the largest amount of energy when gaining an electron, we need to analyze the electron gain enthalpy of the elements provided: oxygen (O), sulfur (S), selenium (Se), and tellurium (Te).

### Step-by-Step Solution:

1. **Understanding Electron Gain Enthalpy**:
- Electron gain enthalpy is the energy released when an electron is added to a neutral atom to form an anion. A more negative value indicates a greater release of energy.

2. **Trends in the Periodic Table**:
- As we move down a group in the periodic table, the atomic size increases due to the addition of electron shells. This generally leads to a decrease in the attraction between the nucleus and the added electron, resulting in a less negative electron gain enthalpy.

3. **Analyzing the Given Elements**:
- **Oxygen (O)**: It has a small atomic size and a high nuclear charge, which would typically suggest a high electron gain enthalpy. However, due to its small size, the addition of an electron leads to significant inter-electronic repulsion among the existing electrons, which reduces the energy released.
- **Sulfur (S)**: Larger than oxygen, sulfur has a more favorable environment for gaining an electron without significant repulsion, resulting in a higher release of energy compared to oxygen.
- **Selenium (Se)** and **Tellurium (Te)**: These elements are even larger than sulfur, and while they have lower nuclear charge, they also have lower electron gain enthalpy values due to their larger size and increased distance from the nucleus.

4. **Comparing Electron Gain Enthalpy**:
- The general trend would suggest that sulfur would have the highest electron gain enthalpy among the given elements, followed by selenium, oxygen, and then tellurium.

5. **Conclusion**:
- Despite oxygen's high nuclear charge, its small size and the resulting inter-electronic repulsion mean that it does not have the highest energy release when gaining an electron. Therefore, sulfur has the largest energy released when gaining an electron.

### Final Answer:
The element that releases the largest amount of energy on gaining an electron is **Sulfur (S)**.