Electron affinity is positive when

Options

A. O changes into `O^(-)`
B. `O^(-)` changes into `O^(2-)`
C. O changes into `O^(+)`
D. electron affinity is always negative

Explanation

**Step-by-Step Solution:**

1. **Understanding Electron Affinity**: Electron affinity refers to the amount of energy released or absorbed when an electron is added to a neutral atom in the gas phase. It is a measure of the tendency of an atom to accept an electron.

2. **Defining Positive Electron Affinity**: Electron affinity is considered positive when the process of adding an electron to an atom requires energy instead of releasing energy. This typically occurs when the atom already has a negative charge or when there are significant repulsive forces between electrons.

3. **Example with Oxygen**: For instance, when we add an electron to an oxygen atom that already has a negative charge (O⁻), it becomes O²⁻. In this case, the two negatively charged species (O⁻ and the incoming electron) will repel each other due to electrostatic repulsion. As a result, energy must be supplied to overcome this repulsion, making the process endothermic.

4. **Conclusion**: Therefore, when electron affinity is positive, it indicates that energy is required to add an electron to an atom, often due to repulsive forces between electrons. This is the case for elements that already have a negative charge or for those where electron-electron repulsions are significant.

**Final Answer**: Electron affinity is positive when energy is required to add an electron to an atom, often due to repulsive forces between electrons.

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