The basic strength of which hydroxide is maximum?

Options

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

Explanation

To determine which hydroxide has the maximum basic strength among the alkali metal hydroxides (LiOH, NaOH, KOH, RbOH, CsOH), we can follow these steps:

### Step 1: Understand Basic Strength
Basic strength refers to the ability of a compound to donate hydroxide ions (OH-) in solution. The more readily a hydroxide can release OH- ions, the stronger the base.

### Step 2: Identify the Alkali Metals
The alkali metals in order of increasing atomic number are:
- Lithium (Li)
- Sodium (Na)
- Potassium (K)
- Rubidium (Rb)
- Cesium (Cs)

### Step 3: Analyze Atomic Size and Z-effective
As we move down the group from Li to Cs, the atomic size increases. This increase in size leads to a decrease in the effective nuclear charge (Z-effective) experienced by the outermost electrons.

### Step 4: Relate Atomic Size to Basic Strength
- A larger atomic size means that the bond between the metal ion (M+) and the hydroxide ion (OH-) becomes weaker.
- For smaller alkali metals like lithium, the bond with OH- is stronger due to better overlap of orbitals, making it less likely to release OH- ions.
- Conversely, for larger alkali metals like cesium, the bond is weaker, allowing OH- to be released more readily.

### Step 5: Conclusion on Basic Strength
Based on the above analysis, we can conclude:
- **Cesium hydroxide (CsOH)** has the maximum basic strength because it can easily release OH- ions due to the weak bond formed between the large Cs+ ion and the OH- ion.

### Final Answer
The hydroxide with the maximum basic strength is **Cesium Hydroxide (CsOH)**.

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