Which of the following processes involves absorption of energy?

Options

A. `S(g)+e^(-) to S^(-)(g)`
B. `S^(-)+e^(-) to S^(2-)(g)`
C. `Cl(g)+e^(-) to Cl^(-)(g)`
D. none of these

Answer

To determine which of the following processes involves the absorption of energy, we need to analyze the reactions provided. The key concept here is the electron gain enthalpy, which is the energy change that occurs when an atom gains an electron.

### Step-by-Step Solution:

1. **Understanding Electron Gain Enthalpy**:
- When an atom gains an electron, energy is typically released. This is because the process of gaining an electron is usually exothermic, meaning it has a negative electron gain enthalpy.

2. **Identifying the Processes**:
- We need to look at the specific processes given in the options. The reactions generally involve either neutral atoms or anions.

3. **Analyzing the Anion Reaction**:
- Consider the reaction where an anion is formed by adding an electron to an already negatively charged ion (anion). For example, if we have \( S^{-} + e^{-} \rightarrow S^{2-} \):
- Here, \( S^{-} \) is an anion, and when we add another electron, we are increasing the negative charge.
- This leads to increased electron-electron repulsions because like charges repel each other.

4. **Energy Absorption in Anion Formation**:
- To overcome these repulsions when adding an electron to an anion, energy must be absorbed. This is because the system requires energy to counteract the repulsive forces between the electrons.

5. **Conclusion**:
- Therefore, the process that involves the absorption of energy is the one where an electron is added to an anion, which is option 2 in the question.

### Final Answer:
The process that involves absorption of energy is **option 2** (adding an electron to an anion).