The correct order of increasing electron affinity of the following elements is:

Options

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

Answer

To determine the correct order of increasing electron affinity for the elements mentioned (Oxygen, Sulfur, Fluorine, and Chlorine), we will follow these steps:

### Step 1: Understand Electron Affinity
Electron affinity is the measure of the energy change when an electron is added to a neutral atom in the gas phase. A higher electron affinity means that the atom has a greater tendency to gain an electron.

### Step 2: Identify the Groups and Periods
- Oxygen (O) and Sulfur (S) are in Group 16 (Chalcogens).
- Fluorine (F) and Chlorine (Cl) are in Group 17 (Halogens).

### Step 3: Analyze Trends in Electron Affinity
- **Down a Group**: As we move down a group, the size of the atoms increases, and the nuclear charge experienced by the outermost electrons decreases. Therefore, electron affinity generally decreases down a group.
- **Across a Period**: As we move from left to right across a period, the nuclear charge increases, leading to a higher tendency to gain electrons. Thus, electron affinity generally increases across a period.

### Step 4: Compare Electron Affinities of the Elements
- **Fluorine (F)**: Although it is highly electronegative, its small size leads to electron-electron repulsion when gaining an electron, which can lower its electron affinity compared to Chlorine.
- **Chlorine (Cl)**: Larger than Fluorine, it has a higher electron affinity because it can accommodate an additional electron more easily.
- **Oxygen (O)**: Smaller than Sulfur and has a high electronegativity, but its small size leads to repulsion when gaining an electron.
- **Sulfur (S)**: Larger than Oxygen, thus it has a higher electron affinity than Oxygen.

### Step 5: Order the Electron Affinities
Based on the analysis:
- Chlorine (Cl) has the highest electron affinity.
- Fluorine (F) has a lower electron affinity than Chlorine but higher than Oxygen and Sulfur.
- Sulfur (S) has a higher electron affinity than Oxygen (O).

### Final Order of Increasing Electron Affinity
Thus, the correct order of increasing electron affinity for the elements is:
**Oxygen (O) < Sulfur (S) < Fluorine (F) < Chlorine (Cl)**

### Conclusion
The correct answer is: **O < S < F < Cl**