Element which has most negative electron gain enthalpy is

Options

A. F
B. O
C. Cl
D. S

Answer

To determine which element has the most negative electron gain enthalpy among the options provided (Fluorine, Oxygen, Chlorine, and Sulfur), we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Electron Gain Enthalpy**:
- Electron gain enthalpy is the energy change that occurs when an electron is added to a neutral atom in the gaseous state. A more negative value indicates a greater tendency to gain an electron and achieve a stable electronic configuration.

2. **Trends in the Periodic Table**:
- As you move from left to right across a period in the periodic table, the electron gain enthalpy becomes more negative. This is due to increasing nuclear charge, which attracts the added electron more strongly.
- As you move down a group, the electron gain enthalpy becomes less negative. This is because the atomic size increases, and the added electron is further from the nucleus, leading to decreased attraction.

3. **Analyzing the Given Elements**:
- The elements given are Fluorine (F), Oxygen (O), Chlorine (Cl), and Sulfur (S).
- Their positions in the periodic table are:
- Oxygen (O) - Group 16, Period 2
- Fluorine (F) - Group 17, Period 2
- Chlorine (Cl) - Group 17, Period 3
- Sulfur (S) - Group 16, Period 3

4. **Comparing Electron Gain Enthalpies**:
- Fluorine has a higher electron gain enthalpy than Chlorine despite being in the same group. This is because Fluorine is smaller, leading to greater electron-electron repulsion when it gains an electron.
- Chlorine, being larger, experiences less repulsion upon gaining an electron, making it more stable in that state.

5. **Conclusion**:
- Among the options, Chlorine has the most negative electron gain enthalpy, as it is more stable when gaining an electron compared to Fluorine, Oxygen, and Sulfur.

### Final Answer:
The element which has the most negative electron gain enthalpy is **Chlorine (Cl)**.