The process requiring the absorption of energy is (are):

Options

A. Cl-`Cl^-`
B. `O^(-)toO^(2-)`
C. `Fe^(2+)toFe^(3+)`
D. `ArtoAr^(-)`

Explanation

To determine which processes require the absorption of energy, we need to analyze each option based on the concept of electron affinity and ionization energy.

### Step-by-Step Solution:

1. **Understanding Electron Affinity**:
- Electron affinity is the amount of energy released when an electron is added to a neutral atom in the gas phase.
- The first electron affinity is typically negative for most elements, meaning energy is released when an electron is added. However, for inert gases, energy must be absorbed to add an electron because they already have a complete octet.

2. **Analyzing the Processes**:
- **Process 1: Cl to Cl⁻**:
- This involves adding an electron to chlorine. Since chlorine is not an inert gas, energy is released in this process.
- **Energy Requirement**: No energy absorption required (energy released).

- **Process 2: O⁻ to O²⁻**:
- Here, we are adding an electron to an already negatively charged oxygen ion. This requires energy because of electron-electron repulsion.
- **Energy Requirement**: Energy absorption required.

- **Process 3: Fe²⁺ to Fe³⁺**:
- This process involves removing an electron from Fe²⁺ to form Fe³⁺. Removing an electron requires energy (ionization energy).
- **Energy Requirement**: Energy absorption required.

- **Process 4: Ar to Ar⁻**:
- Adding an electron to argon (an inert gas) requires energy because argon already has a complete octet. Thus, energy must be absorbed to destabilize it.
- **Energy Requirement**: Energy absorption required.

3. **Conclusion**:
- The processes that require the absorption of energy are:
- O⁻ to O²⁻
- Fe²⁺ to Fe³⁺
- Ar to Ar⁻

### Final Answer:
The processes requiring the absorption of energy are:
- O⁻ to O²⁻
- Fe²⁺ to Fe³⁺
- Ar to Ar⁻