Which of the following processes is exothermic?

Options

A. `O rarr O^(-)`
B. `O^(-) rarr O^(2-)`
C. `S^(-) rarr S^(2-)`
D. `Li rarr Li^(+)`

Answer

To determine which of the following processes is exothermic, we need to understand the definition of exothermic reactions. An exothermic process is one that releases energy, usually in the form of heat.

Let's analyze the given processes step by step:

### Step 1: Understand the processes
1. **Formation of O- from O + e-**: This process involves adding an electron to a neutral oxygen atom to form a negatively charged ion (O-).
2. **Formation of O2- from O- + e-**: This process involves adding another electron to the O- ion to form O2-.
3. **Formation of S2- from S- + e-**: This process involves adding an electron to a negatively charged sulfur ion (S-) to form S2-.
4. **Ionization of Li (Li → Li+ + e-)**: This process involves removing an electron from a neutral lithium atom to form a positively charged ion (Li+).

### Step 2: Analyze each process for exothermicity
1. **O + e- → O-**: This process is exothermic because energy is released when an electron is added to a neutral atom. This is similar to the electron gain enthalpy, which is negative, indicating that energy is released.

2. **O- + e- → O2-**: This process is endothermic because adding an electron to a negatively charged ion (O-) requires energy to overcome the repulsion between the two negative charges.

3. **S- + e- → S2-**: Similar to the previous step, this process is also endothermic because it involves adding an electron to a negatively charged sulfur ion, which also requires energy to overcome repulsion.

4. **Li → Li+ + e-**: This process is endothermic because it requires energy to remove an electron from a neutral lithium atom.

### Step 3: Conclusion
After analyzing all the processes, we find that the only exothermic process is the formation of O- from O + e-. Therefore, the answer to the question is:

**The exothermic process is: O + e- → O-**