The correct order of ionic size in polar solvent is

Options

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

Answer

To determine the correct order of ionic size in a polar solvent for the given group 1 cations (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺), we can follow these steps:

### Step 1: Identify the Cations
The cations we are considering from group 1 are:
- Lithium (Li⁺)
- Sodium (Na⁺)
- Potassium (K⁺)
- Rubidium (Rb⁺)
- Cesium (Cs⁺)

### Step 2: Understand Ionic Size Trends
As we move down the group in the periodic table, the ionic size increases. This is due to the addition of electron shells, which increases the distance between the nucleus and the outermost electrons. Thus, the order of ionic sizes for these cations in terms of size is:
- Li⁺ < Na⁺ < K⁺ < Rb⁺ < Cs⁺

### Step 3: Consider Hydration Energy
When cations are placed in a polar solvent, they interact with the solvent molecules. The smaller the cation, the higher the hydration energy, as it can attract more solvent molecules due to its higher charge density. This means that smaller cations will be more effectively surrounded by solvent molecules.

### Step 4: Establish the Order in Polar Solvent
In a polar solvent, the effective size of the cation can be influenced by its hydration. The order of ionic size in a polar solvent will still follow the trend of ionic size but will also consider how well they are hydrated. The order of ionic size in polar solvent remains:
- Li⁺ < Na⁺ < K⁺ < Rb⁺ < Cs⁺

### Conclusion
Thus, the correct order of ionic size in a polar solvent is:
**Li⁺ < Na⁺ < K⁺ < Rb⁺ < Cs⁺**