In which case the energy released is minimum -

Options

A. `Cl to Cl^(-)`
B. `P to P^(-)`
C. `N to N^(-)`
D. `C to C^(-)`

Answer

To determine in which case the energy released is minimum when adding an electron to an atom (i.e., the electron affinity), we can analyze the electron affinities of the given elements: chlorine, phosphorus, nitrogen, and carbon.

### Step-by-Step Solution:

1. **Understanding Electron Affinity**:
- Electron affinity is the energy change that occurs when an electron is added to a neutral atom in the gas phase. A more negative value indicates a greater release of energy (more favorable).

2. **Identify the Elements**:
- The elements in question are chlorine (Cl), phosphorus (P), nitrogen (N), and carbon (C).

3. **Determine the Electronic Configuration**:
- Chlorine (Cl, atomic number 17): 1s² 2s² 2p⁶ 3s² 3p⁵
- Phosphorus (P, atomic number 15): 1s² 2s² 2p⁶ 3s² 3p³
- Nitrogen (N, atomic number 7): 1s² 2s² 2p³
- Carbon (C, atomic number 6): 1s² 2s² 2p²

4. **Analyze the Stability of the Configurations**:
- Chlorine achieves a noble gas configuration (3s² 3p⁶) upon gaining an electron, which is highly stable.
- Phosphorus has a half-filled p subshell (3s² 3p³), which is relatively stable but less so than chlorine.
- Nitrogen also has a half-filled p subshell (2s² 2p³), which is stable, but it has a lower effective nuclear charge compared to phosphorus.
- Carbon, with a configuration of 2s² 2p², is less stable than nitrogen and phosphorus when gaining an electron.

5. **Trend of Electron Affinity**:
- Generally, electron affinity increases across a period (left to right) and decreases down a group (top to bottom).
- However, half-filled and fully filled subshells are particularly stable, which can affect the trend.

6. **Comparing Electron Affinities**:
- Chlorine will have the highest electron affinity due to its ability to achieve a stable noble gas configuration.
- Phosphorus and nitrogen both have half-filled configurations, but phosphorus has a higher effective nuclear charge, making it more favorable to gain an electron than nitrogen.
- Carbon has a lower electron affinity than nitrogen because it does not benefit from a half-filled configuration upon gaining an electron.

7. **Conclusion**:
- Among the elements, nitrogen will have the minimum energy release (least negative electron affinity) when gaining an electron because of its stable half-filled p subshell and lower effective nuclear charge compared to phosphorus.

### Final Answer:
**The element with minimum energy released upon gaining an electron is Nitrogen (N).**

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