The elements of group 1 describe, more clearly then only group of elements, the effects of increasing the size of atoms or ions on the physical and chemical properties.The chemical and physical properties of the elements are closely related to their electronic structures and sizes.These metals are highly electropositive and thus form very strong bases, and have quite stable oxo-salts.In the manufacturing of sodium hydroxide, chlorine and sodium carbonate, the sodium chloride is used as starting material.
Which of the following has the highest solubility in water ?

Options

A. LiOH
B. KOH
C. CsOH
D. RbOH

Explanation

To determine which hydroxide of the alkali metals has the highest solubility in water, we can follow these steps:

### Step-by-Step Solution

1. **Understand the Group 1 Elements**: The alkali metals (Group 1) include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs). These metals are characterized by their high electropositivity and the ability to form strong bases.

2. **Identify the Hydroxides**: The hydroxides of these alkali metals are:
- Lithium hydroxide (LiOH)
- Sodium hydroxide (NaOH)
- Potassium hydroxide (KOH)
- Rubidium hydroxide (RbOH)
- Cesium hydroxide (CsOH)

3. **Consider Ionization Enthalpy**: The ionization enthalpy of alkali metals decreases as we move down the group. This means that it becomes easier to remove an electron from the metal as we go from lithium to cesium.

4. **Bond Strength in Hydroxides**: The bond between the metal (M) and the hydroxide (OH) in the hydroxides is represented as MOH. As the size of the metal ion increases down the group, the bond strength of the MOH bond decreases, making it easier for the bond to break.

5. **Basic Strength and Solubility**: As the ionization enthalpy decreases and the bond strength of MOH decreases, the basic strength of the hydroxides increases. Higher basic strength correlates with higher solubility in water.

6. **Rank the Hydroxides**: Based on the above points, we can rank the solubility of the hydroxides in water:
- LiOH (least soluble)
- NaOH
- KOH
- RbOH
- CsOH (most soluble)

7. **Conclusion**: Therefore, cesium hydroxide (CsOH) has the highest solubility in water among the alkali metal hydroxides.

### Final Answer
**Cesium hydroxide (CsOH)** has the highest solubility in water.

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