The element with the lowest `IE_(1)` is :

Options

A. sodium
B. cesiusm
C. barium
D. magnesium

Answer

To determine the element with the lowest first ionization energy (IE₁), we can follow these steps:

### Step-by-Step Solution:

1. **Understand Ionization Energy**:
- Ionization energy is the amount of energy required to remove an electron from an atom in its gaseous state. The first ionization energy (IE₁) refers to the energy needed to remove the first electron.

2. **Locate Elements in the Periodic Table**:
- Identify the elements in the periodic table. The periodic table is organized into groups (columns) and periods (rows). Elements in the same group have similar properties.

3. **Trends in Ionization Energy**:
- Ionization energy generally increases across a period (from left to right) and decreases down a group (from top to bottom). This is because:
- Across a period, the atomic size decreases, leading to a stronger attraction between the nucleus and the electrons.
- Down a group, the atomic size increases, resulting in a weaker attraction between the nucleus and the outermost electrons, making it easier to remove an electron.

4. **Identify the Elements of Interest**:
- For this question, we focus on elements from Group 1 (alkali metals) and Group 2 (alkaline earth metals) as they typically have lower ionization energies compared to other groups.
- The relevant elements are: Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), and Cesium (Cs) from Group 1, and Beryllium (Be), Magnesium (Mg), Calcium (Ca), and Barium (Ba) from Group 2.

5. **Compare the Sizes and Ionization Energies**:
- Among the alkali metals, as we move down the group from Lithium to Cesium, the atomic size increases, and thus the ionization energy decreases.
- Cesium (Cs) is the largest atom among the alkali metals, meaning it has the weakest hold on its outermost electron.

6. **Conclusion**:
- Therefore, Cesium (Cs) has the lowest first ionization energy (IE₁) among the elements considered.

### Final Answer:
The element with the lowest first ionization energy (IE₁) is **Cesium (Cs)**.

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