Which of the following would require least energy?

Options

A. `Si^(-)(g) rarr Si(g)+e^(-)`
B. `P^(-)(g)rarr P(g)+e^(-)`
C. `S^(-)(g) rarr S(g) +e^(-)`
D. `CI^(-)(g) rarr CI(g) +e^(-)`

Answer

To determine which of the given elements requires the least energy to remove an electron, we will analyze the ionization energy trends and the stability of the resulting species after the removal of an electron.

### Step-by-step Solution:

1. **Understanding Ionization Energy**:
- Ionization energy (IE) is the energy required to remove an electron from an atom in its gaseous state.
- Generally, ionization energy increases across a period (left to right) and decreases down a group (top to bottom) in the periodic table.

2. **Analyzing the Elements**:
- We are given silicon (Si), sulfur (S), and chlorine (Cl) as options. We need to consider their positions in the periodic table and their electron configurations.
- Silicon (Si) is in group 14, sulfur (S) is in group 16, and chlorine (Cl) is in group 17.

3. **Stability of the Resulting Species**:
- When an electron is removed from an atom, the stability of the resulting ion plays a crucial role in determining the energy required.
- For sulfur, if we remove an electron from S²⁻ (which has a stable electron configuration), it becomes S³⁻, which is less stable. The process is favorable because the resulting ion is more stable.
- For chlorine, removing an electron from Cl⁻ (which is also stable) results in Cl, which is less stable than Cl⁻.

4. **Comparing Ionization Energies**:
- Silicon has a higher ionization energy compared to sulfur and chlorine due to its position in the periodic table.
- Sulfur, with its stable negative ion (S²⁻), will require less energy to remove an electron compared to silicon and chlorine.

5. **Conclusion**:
- Based on the analysis, the element that would require the least energy to remove an electron is **sulfur (S)**.

### Final Answer:
The element that would require the least energy to remove an electron is **sulfur (S)**.