Which one of the following arrangements represents the correct order of least negative to most negative electron gain enthalpy for C, Ca, Al , F and O ?

Options

A. `Al lt Ca lt O lt C lt F`
B. `Al lt O lt C lt Ca lt F`
C. `C lt F lt O lt Al lt Ca`
D. `Ca lt Al lt C lt O lt F`

Answer

To determine the correct order of least negative to most negative electron gain enthalpy for the elements C (Carbon), Ca (Calcium), Al (Aluminum), F (Fluorine), and O (Oxygen), we need to consider the trends in electron gain enthalpy across periods and down groups in the periodic table.

### Step-by-Step Solution:

1. **Understanding Electron Gain Enthalpy (EGE)**:
- Electron gain enthalpy is the amount of energy released 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.

2. **Trends in the Periodic Table**:
- **Across a Period**: As we move from left to right across a period, the electron gain enthalpy becomes more negative (i.e., more energy is released) due to increased nuclear charge attracting the added electron more strongly.
- **Down a Group**: As we move down a group, the electron gain enthalpy becomes less negative (i.e., less energy is released) because the atomic size increases, leading to a weaker attraction between the nucleus and the added electron.

3. **Analyzing the Given Elements**:
- **Fluorine (F)**: Highest electron gain enthalpy because it is on the right side of the periodic table and has a high nuclear charge.
- **Oxygen (O)**: Next in line; it also has a high electron gain enthalpy but is less than that of Fluorine.
- **Carbon (C)**: Has a lower electron gain enthalpy than Oxygen because it is further left in the periodic table.
- **Aluminum (Al)**: Lower than Carbon; being in the third period, it has less tendency to gain an electron compared to the elements in the second period.
- **Calcium (Ca)**: Lowest electron gain enthalpy among these elements as it is further down the group and has a larger atomic size.

4. **Arranging the Elements**:
- Based on the analysis, we can arrange the elements from least negative to most negative electron gain enthalpy:
- Calcium (Ca) < Aluminum (Al) < Carbon (C) < Oxygen (O) < Fluorine (F)

5. **Final Order**:
- The correct order of least negative to most negative electron gain enthalpy is:
- Ca < Al < C < O < F

### Conclusion:
Thus, the correct arrangement representing the order of least negative to most negative electron gain enthalpy for C, Ca, Al, F, and O is:
**Ca < Al < C < O < F**