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

Options

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

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 will follow these steps:

### Step 1: Understand Electron Gain Enthalpy
Electron gain enthalpy is defined as the amount of energy released when an electron is added to a neutral gaseous atom. A more negative value indicates a greater tendency to accept an electron.

### Step 2: Analyze the Elements
The elements given are:
- Carbon (C)
- Calcium (Ca)
- Aluminum (Al)
- Fluorine (F)
- Oxygen (O)

### Step 3: Position in the Periodic Table
- **Calcium (Ca)**: Group 2, Period 4 (alkaline earth metal)
- **Aluminum (Al)**: Group 13, Period 3 (p-block element)
- **Carbon (C)**: Group 14, Period 2 (p-block element)
- **Oxygen (O)**: Group 16, Period 2 (p-block element)
- **Fluorine (F)**: Group 17, Period 2 (p-block element)

### Step 4: Trend of Electron Gain Enthalpy
1. **Down a Group**: Electron gain enthalpy becomes less negative (less favorable) as you move down a group due to increased atomic size and shielding effect.
2. **Across a Period**: Electron gain enthalpy becomes more negative (more favorable) as you move from left to right across a period due to increased nuclear charge attracting the added electron more effectively.

### Step 5: Compare the Elements
- **Calcium (Ca)**: Least negative electron gain enthalpy because it tends to lose electrons rather than gain them.
- **Aluminum (Al)**: More negative than Ca but less negative than C, O, and F.
- **Carbon (C)**: Has a moderate tendency to gain an electron.
- **Oxygen (O)**: More negative than C, as it is more electronegative and attracts electrons more effectively.
- **Fluorine (F)**: Most negative electron gain enthalpy due to its high electronegativity and small atomic size.

### Step 6: Arrange the Elements
Based on the analysis:
- **Least negative**: Calcium (Ca)
- Aluminum (Al)
- Carbon (C)
- Oxygen (O)
- **Most negative**: Fluorine (F)

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