The electron affinity of the member of oxygen of the periodic table, follows the sequence

Options

A. O gt S gt Se
B. S gt O lt Se
C. O lt S gt Se
D. Se 'gt' O gt S

Answer

To determine the electron affinity of the members of the oxygen group in the periodic table (Oxygen, Sulfur, and Selenium), we need to analyze the trends in electron affinity based on their atomic structure and position in the periodic table.

### Step-by-Step Solution:

1. **Identify the Elements**: The elements in question are Oxygen (O), Sulfur (S), and Selenium (Se). Their atomic numbers are:
- Oxygen (O): 8
- Sulfur (S): 16
- Selenium (Se): 34

2. **Determine the Electronic Configuration**:
- Oxygen: 1s² 2s² 2p⁴
- Sulfur: [Ne] 3s² 3p⁴
- Selenium: [Ar] 3d¹⁰ 4s² 4p⁴

3. **Identify the Periods**:
- Oxygen is in Period 2.
- Sulfur is in Period 3.
- Selenium is in Period 4.

4. **Understand the Group**: All three elements belong to Group 16 of the periodic table (the chalcogens).

5. **Analyze the Trend in Electron Affinity**:
- As we move down the group from Oxygen to Selenium, the atomic size increases. This leads to a decrease in the effective nuclear charge experienced by the added electron due to increased distance from the nucleus.
- Consequently, the ability of the nucleus to attract additional electrons diminishes.

6. **Consider Electron-Electron Repulsion**:
- Oxygen has a small atomic radius, and when an electron is added to form O⁻, there is significant electron-electron repulsion due to the high charge density. This makes the addition of a second electron (to form O²⁻) endothermic, resulting in a low or even positive electron affinity for oxygen.
- In contrast, Sulfur and Selenium, while still experiencing some repulsion, have larger atomic radii, which mitigates this effect somewhat.

7. **Establish the Order of Electron Affinity**:
- Based on the above analysis, we can conclude that:
- Oxygen has the least electron affinity (it may even be positive).
- Sulfur has a more negative electron affinity than oxygen but less than selenium.
- Selenium has the most negative electron affinity among the three.

8. **Final Order**: Thus, the order of electron affinity from highest to lowest is:
- **Selenium (Se) > Sulfur (S) > Oxygen (O)**

### Conclusion:
The correct order of electron affinity for the members of the oxygen group is:
**Se > S > O**