Which of the following transformation least energy is required?

Options

A. `F_((g))^(-)to F_((g))+e^(-)`
B. `P_((g))^(-) to P_((g))+e^(-)`
C. `S_((g))^(-) to S_((g))+e^(-)`
D. `Cl_((g))^(-) to Cl_((g))+e^(-)`

Explanation

To determine which transformation requires the least energy, we need to analyze the electron gain enthalpy of different elements and their ability to gain electrons. Here’s a step-by-step solution:

### Step 1: Understand Electron Gain Enthalpy
Electron gain enthalpy is the amount of energy released when an electron is added to an atom in the gas phase. A more negative value indicates that more energy is released, meaning the process is more favorable.

### Step 2: Identify the Elements
The elements mentioned are fluorine (F), phosphorus (P), sulfur (S), and chlorine (Cl). We need to compare their electron gain enthalpies.

### Step 3: Analyze the Trends
1. **Across a Period**: As we move from left to right across a period, the size of the atoms decreases, and the electron gain enthalpy becomes more negative (more energy is released).
2. **Down a Group**: As we move down a group, the size of the atoms increases, and the electron gain enthalpy becomes less negative (less energy is released).

### Step 4: Compare the Elements
- **Fluorine (F)**: Has a high electron gain enthalpy due to its small size and high electronegativity, but it also experiences significant electron-electron repulsion when gaining an electron.
- **Chlorine (Cl)**: Larger than fluorine, so it has a less negative electron gain enthalpy compared to fluorine.
- **Sulfur (S)**: Larger than chlorine, thus it has an even less negative electron gain enthalpy.
- **Phosphorus (P)**: The largest among these elements, leading to the least negative electron gain enthalpy.

### Step 5: Determine the Least Energy Required
Since we are looking for the transformation that requires the least energy, we should focus on the element that has the least negative electron gain enthalpy. This would be phosphorus (P), as it is the largest atom and thus has the weakest attraction for an additional electron.

### Conclusion
The transformation that requires the least energy is the addition of an electron to phosphorus (P).