The solubility of most of the alkali metal halides except those of ___ decreases on descending the group.

Options

A. `NaClgt KCl gt RbClgt CsCl`
B. `CsCl gt RbCl gt KCl gt NaCl`
C. `KCl gt NaCl gt RbCl gt CsCl`
D. `CsCl gt RbCl gt NaCl gt KCl`

Answer

To solve the question regarding the solubility of alkali metal halides, we can follow these steps:

### Step 1: Understand the General Trend
The question asks about the solubility of alkali metal halides as we move down the group in the periodic table. Generally, the solubility of most alkali metal halides decreases as we descend the group.

**Hint:** Consider the periodic trends in solubility for alkali metal compounds.

### Step 2: Identify the Exception
We need to identify which specific halide does not follow this trend. The halides in question are fluorides, chlorides, bromides, and iodides.

**Hint:** Recall the specific behavior of fluorides in comparison to other halides.

### Step 3: Analyze the Solubility of Fluorides
Fluorides are known to be an exception. As we move down the group, the solubility of alkali metal fluorides actually increases. This is contrary to the trend observed in chlorides, bromides, and iodides.

**Hint:** Think about the factors affecting solubility, such as hydration enthalpy.

### Step 4: Relate Hydration Enthalpy to Solubility
The solubility of salts is influenced by hydration enthalpy. For alkali metal fluorides, the hydration enthalpy increases down the group, which contributes to their increased solubility. In contrast, for chlorides, bromides, and iodides, the hydration enthalpy decreases down the group, leading to decreased solubility.

**Hint:** Consider how the size of the ions and their interactions with water molecules affect solubility.

### Step 5: Conclude the Answer
Based on the analysis, we conclude that the solubility of most alkali metal halides decreases down the group, except for the fluorides.

**Final Answer:** The solubility of most of the alkali metal halides except those of **fluorides** decreases on descending the group.