In the given below alkali metal ions which has lowest ionic mobility in aqueous solutions?

Options

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

Answer

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 under the influence of an electric field. It is influenced by the size of the ion and its hydration.

**Hint:** Ionic mobility is affected by both the size of the ion and how well it interacts with water molecules.

### Step 2: Consider the Alkali Metal Ions
The alkali metal ions we need to consider are:
- Lithium (Li⁺)
- Sodium (Na⁺)
- Potassium (K⁺)
- Rubidium (Rb⁺)
- Cesium (Cs⁺)

**Hint:** List the alkali metals in order of increasing atomic number to see how their ionic sizes change.

### Step 3: Analyze Ionic Sizes
As we move down the group in the periodic table from lithium to cesium, the ionic radius increases. This means that cesium (Cs⁺) is the largest ion, while lithium (Li⁺) is the smallest.

**Hint:** Remember that larger ions tend to have lower charge density, which affects their mobility.

### Step 4: Hydration of Ions
Hydration refers to the process where water molecules surround and interact with ions. Smaller ions, like Li⁺, have a higher charge density and can attract more water molecules, leading to greater hydration.

**Hint:** The degree of hydration is inversely related to the size of the ion; smaller ions are more hydrated.

### Step 5: Relate Size and Mobility
Since larger ions are less hydrated, they tend to have higher mobility. Conversely, smaller ions, which are more hydrated, have lower mobility. Therefore, as the size of the ion increases, its mobility decreases.

**Hint:** Think about how the interaction of ions with water molecules affects their movement.

### Step 6: Conclusion
Among the alkali metal ions, lithium (Li⁺) is the smallest and most hydrated ion, which results in it having the lowest ionic mobility in aqueous solutions.

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

**Correct Option:** C