Which of the following is energy releasing process ?

Options

A. `X^(-) to X (g) +e^(-)`
B. `O^(-)(g) +e^(-) to O^(2-)`
C. `O(g) to O^(+)(g) +e^(-)`
D. `O(g) +e^(-) to O^(-) (g)`

Explanation

To determine which of the given processes is energy-releasing, we need to understand the concepts of ionization enthalpy and electron affinity.

### Step-by-Step Solution:

1. **Understand the Terms**:
- **Ionization Enthalpy**: This is the energy required to remove an electron from an atom or ion. It is always a positive value because energy is absorbed to remove an electron.
- **Electron Affinity**: This is the energy change that occurs when an electron is added to a neutral atom. It can be either positive or negative. If energy is released when an electron is added, it is considered an exothermic process (energy-releasing).

2. **Analyze the Options**:
- We need to evaluate the options provided in the question to see which one corresponds to an energy-releasing process.
- Options involving ionization enthalpy will not be energy-releasing since energy is consumed to remove an electron.

3. **Compare Electron Affinity Cases**:
- In the case of a neutral atom gaining an electron (electron affinity), energy is released. This means that the process is exothermic, and ΔH (change in enthalpy) is negative.
- In contrast, if an ion (which already has a charge) gains an electron, energy is required to accommodate that electron, making the process endothermic (ΔH is positive).

4. **Identify the Correct Option**:
- From the analysis, we can conclude that the process where a neutral atom gains an electron is the energy-releasing process.
- Therefore, we need to select the option that corresponds to this scenario.

5. **Final Conclusion**:
- The correct answer is the option where a neutral atom gains an electron, which is option D.