Which one of the following amongst each pair will release maximum energy on gaining one electron (A = F, Cl), (B = S, Se), (C = Li, Na)

Options

A. (A) = Cl, (B) = S, (C) = Li
B. (A) = S, (B) = Cl, (C) = Li
C. (A) = Li, (B) = Cl, (C) = S
D. (A) = Cl, (B) = Li, (C) = S

Answer

To solve the question of which element in each pair releases the maximum energy upon gaining one electron, we will analyze the three pairs: A (F, Cl), B (S, Se), and C (Li, Na).

### Step-by-Step Solution:

1. **Pair A: Fluorine (F) vs. Chlorine (Cl)**
- **Electron Gain Enthalpy**: The energy released when an electron is added to an atom is called electron gain enthalpy.
- **Size Consideration**: Fluorine is smaller than chlorine. A smaller atom has a higher effective nuclear charge experienced by the incoming electron, which can lead to greater repulsion.
- **Conclusion**: Chlorine, being larger, can accommodate the incoming electron more easily, resulting in a higher release of energy. Therefore, **Chlorine (Cl)** releases maximum energy in this pair.

2. **Pair B: Sulfur (S) vs. Selenium (Se)**
- **Trend in Groups**: As we move down a group in the periodic table, the electron gain enthalpy generally decreases due to the increasing atomic size and shielding effect.
- **Comparison**: Sulfur is above selenium in the periodic table. Therefore, sulfur has a higher electron gain enthalpy compared to selenium.
- **Conclusion**: **Sulfur (S)** releases maximum energy in this pair.

3. **Pair C: Lithium (Li) vs. Sodium (Na)**
- **Group Trend**: Similar to the previous pair, as we move down the group from lithium to sodium, the electron gain enthalpy decreases.
- **Comparison**: Lithium is smaller than sodium, which means it has a higher electron gain enthalpy.
- **Conclusion**: **Lithium (Li)** releases maximum energy in this pair.

### Final Answer:
- A: Chlorine (Cl)
- B: Sulfur (S)
- C: Lithium (Li)

Thus, the elements that release maximum energy on gaining one electron from each pair are:
- A: Cl
- B: S
- C: Li