Which of the following is most basic ?

Options

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

Answer

To determine which of the following hydroxides is the most basic among the alkali metals, we need to analyze the basicity of their hydroxides: LiOH, NaOH, KOH, RbOH, and CsOH. The basicity of these hydroxides can be understood through their ability to dissociate in water and release hydroxide ions (OH⁻).

### Step-by-Step Solution:

1. **Identify the Alkali Metals**:
The alkali metals in Group 1 of the periodic table include Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), and Cesium (Cs).

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

3. **Understand Basicity**:
Basicity is determined by the ability of a compound to release hydroxide ions (OH⁻) in solution. The more readily a hydroxide dissociates in water to produce OH⁻ ions, the more basic it is.

4. **Dissociation in Water**:
When these hydroxides are dissolved in water, they dissociate as follows:
- LiOH → Li⁺ + OH⁻
- NaOH → Na⁺ + OH⁻
- KOH → K⁺ + OH⁻
- RbOH → Rb⁺ + OH⁻
- CsOH → Cs⁺ + OH⁻

5. **Consider Ionic Character**:
As we move down the group from Li to Cs, the size of the cation increases. Larger cations have a greater ionic character, which means they are more likely to dissociate in solution.

6. **Determine the Most Basic Hydroxide**:
Among the hydroxides, CsOH (Cesium hydroxide) is the most basic because:
- Cs⁺ is a larger cation compared to Li⁺, Na⁺, K⁺, and Rb⁺.
- The larger size of Cs⁺ allows for easier dissociation from OH⁻ ions, leading to a higher concentration of OH⁻ in solution.

7. **Conclusion**:
Therefore, the hydroxide that is the most basic among the given options is **CsOH (Cesium hydroxide)**.