Among the chlorides of alkali metals, what is the decreasing order of hydration ?

Options

A. NaCl > RbCl > LiCl > CsCl
B. LiCl > CsCl >KCl > RbCl >NaCl
C. LiCl > NaCl > KCl > RbCl g>CsCl
D. All are equatlly hydrated as halide is same

Answer

To determine the decreasing order of hydration among the chlorides of alkali metals (LiCl, NaCl, KCl, RbCl, CsCl), we need to consider the factors affecting hydration energy. The hydration energy is influenced by the size of the cation and the charge density.

### Step-by-step Solution:

1. **Understand Alkali Metals and Their Chlorides**:
The alkali metals include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs). Their corresponding chlorides are LiCl, NaCl, KCl, RbCl, and CsCl.

2. **Consider the Size of Cations**:
As we move down the group from lithium to cesium, the size of the cations increases. This means that lithium (Li⁺) is the smallest and cesium (Cs⁺) is the largest.

3. **Hydration Energy Concept**:
Hydration energy is the energy released when ions are surrounded by water molecules. Smaller cations have a higher charge density, which leads to stronger interactions with water molecules.

4. **Order of Hydration Energy**:
Since Li⁺ is the smallest cation, it will have the highest hydration energy. As the size of the cation increases (from Na⁺ to K⁺ to Rb⁺ to Cs⁺), the hydration energy decreases. Therefore, the order of hydration energy is:
- Li⁺ > Na⁺ > K⁺ > Rb⁺ > Cs⁺

5. **Decreasing Order of Hydration for Chlorides**:
The hydration energy directly influences the solubility and stability of the chlorides. Thus, the decreasing order of hydration for the chlorides of alkali metals is:
- LiCl > NaCl > KCl > RbCl > CsCl

### Final Answer:
The decreasing order of hydration among the chlorides of alkali metals is:
**LiCl > NaCl > KCl > RbCl > CsCl**