Which of the following atoms has the lowest ionization potential ?

Options

A. `._(7)^(14)N`
B. `._(55)^(133)Cs`
C. `._(18)^(40)Ar`
D. `._(8)^(16)O`

Explanation

To determine which atom has the lowest ionization potential, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Ionization Potential**:
- Ionization potential (or ionization energy) is defined as the energy required to remove the outermost electron from an atom. The lower the ionization potential, the easier it is to remove an electron.

2. **Consider Atomic Size**:
- Generally, larger atoms have lower ionization potentials because their outermost electrons are farther from the nucleus. This distance reduces the electrostatic attraction between the nucleus and the outermost electron.

3. **Analyze the Given Options**:
- The options provided are nitrogen (N), arsenic (As), oxygen (O), and cesium (Cs).
- **Nitrogen (N)**: A small atom with a relatively high ionization potential.
- **Oxygen (O)**: Also a small atom, with a higher ionization potential than larger atoms.
- **Arsenic (As)**: Larger than nitrogen and oxygen, but still smaller than cesium, thus has a lower ionization potential than N and O.
- **Cesium (Cs)**: The largest atom among the options, with its outermost electron being very far from the nucleus, leading to a very low ionization potential.

4. **Conclusion**:
- Among the options, cesium (Cs) has the lowest ionization potential because its outermost electron is farthest from the nucleus, making it easier to remove.

### Final Answer:
- The atom with the lowest ionization potential is **cesium (Cs)**.