To determine which of the following alkali metals (lithium, sodium, potassium, cesium) is most soluble in water, we can follow these steps:
### Step 1: Identify the Alkali Metals
The alkali metals in question are lithium (Li), sodium (Na), potassium (K), and cesium (Cs). These elements belong to Group 1 of the periodic table.
### Step 2: Understand Hydration Energy
Hydration energy is the energy released when ions are surrounded by water molecules. It is influenced by the size of the ion; smaller ions typically have higher hydration energies because they can interact more strongly with water molecules.
### Step 3: Compare Sizes of the Ions
As we move down the group from lithium to cesium, the size of the alkali metal ions increases:
- Lithium ion (Li⁺) is the smallest.
- Sodium ion (Na⁺) is larger than Li⁺.
- Potassium ion (K⁺) is larger than Na⁺.
- Cesium ion (Cs⁺) is the largest.
### Step 4: Analyze Hydration Energy Trends
Since hydration energy decreases with increasing ionic size, we can conclude that:
- Li⁺ has the highest hydration energy.
- Na⁺ has lower hydration energy than Li⁺.
- K⁺ has lower hydration energy than Na⁺.
- Cs⁺ has the lowest hydration energy among the four.
### Step 5: Determine Solubility in Water
Higher hydration energy leads to greater solubility in water. Therefore, since Li⁺ has the highest hydration energy, lithium compounds (like LiCl or LiClO₄) are expected to be more soluble in water compared to those of sodium, potassium, and cesium.
### Conclusion
The most soluble alkali metal in water among the given options is lithium (Li).
### Final Answer
**Lithium (Li) is the most soluble in water.**
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