Within each pair of element F & Cl s & se, and Li & Na , respectively , the elements that release more energy upon electron gain are

Options

A. Cl , S and Li
B. F, S and Li
C. Cl , Se and Na
D. F, Se and Na

Answer

To determine which element in each pair releases more energy upon gaining an electron, we need to analyze the electron gain enthalpy of each element. The elements in question are:

1. Fluorine (F) and Chlorine (Cl)
2. Sulfur (S) and Selenium (Se)
3. Lithium (Li) and Sodium (Na)

### Step-by-Step Solution:

**Step 1: Analyze Fluorine (F) and Chlorine (Cl)**
- **Fluorine (F)**: Fluorine is the most electronegative element and has a very small atomic size. When an electron is added to fluorine, the electron-electron repulsion becomes significant due to its small size, which can hinder the addition of an electron.
- **Chlorine (Cl)**: Chlorine is larger than fluorine, which means there is less electron-electron repulsion when an electron is added. As a result, chlorine can accommodate an additional electron more easily than fluorine.

**Conclusion for Step 1**: Chlorine (Cl) releases more energy upon gaining an electron than Fluorine (F).

---

**Step 2: Analyze Sulfur (S) and Selenium (Se)**
- **Sulfur (S)**: Sulfur is smaller than selenium and has a higher electronegativity. It can attract electrons more effectively due to its size and electronegativity.
- **Selenium (Se)**: Selenium is larger than sulfur, which means it has a lower tendency to attract electrons compared to sulfur.

**Conclusion for Step 2**: Sulfur (S) releases more energy upon gaining an electron than Selenium (Se).

---

**Step 3: Analyze Lithium (Li) and Sodium (Na)**
- **Lithium (Li)**: Lithium has a smaller atomic size compared to sodium. This smaller size allows lithium to hold onto its electrons more tightly, making it more effective at attracting an additional electron.
- **Sodium (Na)**: Sodium is larger than lithium, which means it has a lower effective nuclear charge acting on the outermost electron. Thus, it is less effective at attracting an additional electron.

**Conclusion for Step 3**: Lithium (Li) releases more energy upon gaining an electron than Sodium (Na).

---

### Final Summary:
- From the pair F & Cl, **Chlorine (Cl)** releases more energy.
- From the pair S & Se, **Sulfur (S)** releases more energy.
- From the pair Li & Na, **Lithium (Li)** releases more energy.