Electron affinity is the

Options

A. The energy required to remove an electron from an isolated atom in its gaseous state
B. The energy released when an electron is added to an isolated atom in its gaseous state
C. The energy required to add an electron to an isolated atom in its gaseous state
D. The ability of an atom to attract an electron

Explanation

**Step-by-Step Solution:**

1. **Understanding Electron Affinity:**
- Electron affinity refers to the energy change that occurs when an electron is added to a neutral atom in the gaseous state. It is a measure of how much an atom wants to gain an electron.

2. **Example with Chlorine:**
- Take chlorine (Cl) as an example. The electronic configuration of chlorine is 1s² 2s² 2p⁶ 3s² 3p⁵, which totals 17 electrons.
- In the valence shell (3s² 3p⁵), chlorine has 5 electrons in the p-orbital and 2 in the s-orbital.

3. **Stability of Electron Configuration:**
- Chlorine has one unpaired electron in the p-orbital, indicating that it can accept one more electron to achieve a stable configuration (3s² 3p⁶), which is the same as the electron configuration of a noble gas (argon).

4. **Energy Release Upon Electron Addition:**
- When chlorine accepts an electron, it becomes more stable. The process of gaining an electron releases energy because the new configuration is more stable than the original state.
- This energy released during the addition of an electron is defined as the electron affinity.

5. **Correct Definition:**
- The correct definition of electron affinity is the energy released when an electron is added to an isolated atom in its gaseous state.

6. **Evaluating Options:**
- Option A: Incorrect, as it states energy is required, which is not true for electron affinity.
- Option B: Correct, as it accurately describes the energy released when an electron is added to an isolated atom in its gaseous state.
- Option C: Incorrect, similar to option A, it states energy is required.
- Option D: Incorrect, as it describes electronegativity, not electron affinity.

**Final Answer:**
The correct definition of electron affinity is the energy released when an electron is added to an isolated atom in its gaseous state.

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