Decreasing order of hydration energy of the following is

Options

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

Answer

To determine the decreasing order of hydration energy for the given alkali metal ions (Li⁺, Na⁺, K⁺, and Cs⁺), we can follow these steps:

### Step-by-Step Solution:

1. **Understand Hydration Energy**: Hydration energy refers to the energy released when ions are surrounded by water molecules. It is influenced by the charge and size of the ion.

2. **Identify the Ions**: The ions given are Li⁺, Na⁺, K⁺, and Cs⁺. These are all alkali metal ions from Group 1 of the periodic table.

3. **Recognize the Trend in Group 1**: As we move down the group from Li to Cs, the size of the ions increases. This is due to the addition of electron shells.

4. **Relate Size to Hydration Energy**: Hydration energy is inversely proportional to the size of the ion when the charge is constant. Since all these ions have a +1 charge, we can focus solely on their sizes.

5. **Order the Ions by Size**: The ionic radii increase in the following order:
- Li⁺ < Na⁺ < K⁺ < Cs⁺
This means that Li⁺ is the smallest and Cs⁺ is the largest.

6. **Determine the Hydration Energy Order**: Since smaller ions have higher hydration energy, the order of hydration energy will be the reverse of the order of size:
- Highest Hydration Energy: Li⁺
- Next: Na⁺
- Then: K⁺
- Lowest Hydration Energy: Cs⁺

7. **Final Order**: Therefore, the decreasing order of hydration energy is:
- Li⁺ > Na⁺ > K⁺ > Cs⁺

### Conclusion:
The correct decreasing order of hydration energy for the given ions is:
**Li⁺ > Na⁺ > K⁺ > Cs⁺**