Which one of the following arrangements represents the correct order of electron gain enthalpy of the given atomic species?
(a)`C l < F < S < O`
(b) `O < S < F < C l`
(c) `S < O < C l < F`
(d) `F < C l < O < S`

Options

A. `CI lt F lt S lt O`
B. ` O lt S lt F lt CI `
C. `S lt O lt CI lt F `
D. `F lt CI lt O lt S `

Answer

To determine the correct order of electron gain enthalpy for the given atomic species (Cl, F, S, O), we will analyze the trends in the periodic table and consider specific exceptions.

### Step-by-Step Solution:

1. **Understanding Electron Gain Enthalpy**:
- Electron gain enthalpy is the energy change when an electron is added to a neutral atom in the gaseous state. It is typically expressed in kilojoules per mole (kJ/mol).
- A more negative value indicates a greater tendency to gain an electron.

2. **Periodic Trends**:
- **Across a Period**: As we move from left to right across a period, the electron gain enthalpy generally increases. This is because atoms become more electronegative and have a stronger attraction for additional electrons.
- **Down a Group**: As we move down a group, the electron gain enthalpy generally decreases. This is due to increased atomic size and shielding effect, which reduces the effective nuclear charge felt by the added electron.

3. **Analyzing the Given Elements**:
- The elements in question are:
- Chlorine (Cl) - Group 17
- Fluorine (F) - Group 17
- Sulfur (S) - Group 16
- Oxygen (O) - Group 16
- Based on the periodic trends:
- F and Cl are halogens, and Cl is larger than F, which can lead to differences in their electron gain enthalpy.
- O and S are chalcogens, and S is larger than O.

4. **Expected Order Based on Trends**:
- Based on the general trends, we would expect:
- Cl > F (due to size)
- S > O (due to size)
- However, we need to consider the exceptions due to atomic size and electron-electron repulsions.

5. **Experimental Values**:
- The experimentally determined values of electron gain enthalpy are:
- Cl: 349 kJ/mol
- F: 333 kJ/mol
- O: 142 kJ/mol
- S: 200 kJ/mol
- From these values, we can see that:
- Cl has the highest electron gain enthalpy, followed by F, then S, and finally O.

6. **Correct Order**:
- Therefore, the correct order of electron gain enthalpy from highest to lowest is:
- Cl > F > S > O
- However, since we are looking for the order in terms of increasing electron gain enthalpy, we can write it as:
- O < S < F < Cl

7. **Final Answer**:
- The correct option from the given choices is (b) O < S < F < Cl.