Which of the following alkali metal ions has the lowest ionic mobility in aqueous solutions?

Options

A. `Li^(o+)`
B. `Na^(o+)`
C. `K^(o+)`
D. `Rb^(o+)`

Explanation

To determine which alkali metal ion has the lowest ionic mobility in aqueous solutions, we can follow these steps:

### Step 1: Understand Ionic Mobility
Ionic mobility refers to the ability of an ion to move through a solution. The higher the mobility, the faster the ion can migrate. In aqueous solutions, ions are surrounded by water molecules, which affects their movement.

**Hint:** Consider how the size of the ion and its interaction with water molecules influence its movement.

### Step 2: Consider Hydration
When an ion is placed in water, it becomes surrounded by water molecules in a process called hydration. The extent of hydration depends on the size of the ion. Smaller ions tend to be more strongly hydrated because they have a higher charge density, which attracts more water molecules.

**Hint:** Think about how the size of the ion affects its ability to attract water molecules.

### Step 3: Compare Alkali Metal Ions
The alkali metal ions include Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺. As we move down the group in the periodic table, the ionic size increases. This means that Li⁺ is the smallest alkali metal ion, followed by Na⁺, K⁺, Rb⁺, and Cs⁺.

**Hint:** Remember that smaller ions have a higher charge density and can attract more water molecules.

### Step 4: Analyze Ionic Mobility
Since Li⁺ is the smallest ion, it will have the highest extent of hydration. This means that it will be surrounded by more water molecules, making it bulkier and less mobile. Conversely, larger ions like Cs⁺ will have lower hydration and thus higher mobility.

**Hint:** Identify which ion is the smallest and how that affects its hydration.

### Step 5: Conclusion
Based on the analysis, Li⁺ has the highest extent of hydration due to its small size, which results in the lowest ionic mobility among the alkali metal ions in aqueous solution.

**Final Answer:** The alkali metal ion with the lowest ionic mobility in aqueous solutions is **Li⁺**.