Which of the alkali metals have the highest density ?

Options

A. Cs
B. Li
C. Na
D. Rb

Answer

To determine which alkali metal has the highest density, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Alkali Metals**: The alkali metals in question are Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), and Cesium (Cs).

2. **Understand Density**: Density is defined as mass per unit volume (Density = Mass/Volume). For elements, density generally increases with an increase in atomic mass, but it also depends on how closely packed the atoms are.

3. **Analyze the Trend in Density**: As we move down the group of alkali metals from Li to Cs, the atomic size increases. This means that while the atomic mass increases, the volume also increases due to the larger atomic size.

4. **Consider the Packing of Atoms**: The larger atomic size leads to less efficient packing of atoms in the solid state, which can affect density. However, the increase in atomic mass tends to outweigh the increase in volume, leading to an overall increase in density down the group.

5. **List the Densities of Alkali Metals**: The densities of the alkali metals are approximately:
- Lithium (Li): 0.534 g/cm³
- Sodium (Na): 0.97 g/cm³
- Potassium (K): 0.89 g/cm³
- Rubidium (Rb): 1.53 g/cm³
- Cesium (Cs): 1.93 g/cm³

6. **Conclusion**: Based on the densities listed, Cesium (Cs) has the highest density among the alkali metals.

### Final Answer:
The alkali metal with the highest density is **Cesium (Cs)**.

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