Which of the chloride shows least solubility in water?

Options

A. LiCl
B. NaCl
C. KCl
D. RbCl

Answer

To determine which chloride shows the least solubility in water among the given alkali metal chlorides (Lithium chloride, Sodium chloride, Potassium chloride, and Rubidium chloride), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Alkali Metal Chlorides**:
The question provides four options: Lithium chloride (LiCl), Sodium chloride (NaCl), Potassium chloride (KCl), and Rubidium chloride (RbCl). All of these are chlorides of alkali metals.

2. **Understand the Trend in Solubility**:
In alkali metal chlorides, the solubility in water generally decreases as we move down the group in the periodic table. This is due to two main factors:
- The increasing atomic size of the cations (Li⁺, Na⁺, K⁺, Rb⁺) as we move down the group.
- The increasing molecular weight of the chlorides as we move down the group.

3. **Analyze the Cation Sizes**:
- Lithium (Li⁺) has the smallest ionic radius, followed by Sodium (Na⁺), Potassium (K⁺), and Rubidium (Rb⁺) which has the largest ionic radius. Smaller cations tend to have higher solubility in water because they can interact more effectively with water molecules.

4. **Consider Molecular Weight**:
- The molecular weight of the chlorides also increases down the group (LiCl < NaCl < KCl < RbCl). Higher molecular weight generally correlates with lower solubility.

5. **Conclusion**:
Based on the trends observed, Rubidium chloride (RbCl) will have the least solubility in water due to its larger ionic size and higher molecular weight compared to the other chlorides listed.

### Final Answer:
Rubidium chloride (RbCl) shows the least solubility in water.