Assertion: Among hydroxides of alkali metals, LiOH is the weakest base.
Reason: Among alkali metals, lithium has the highest ionisation energy .

Options

A. If both assertion and reason are true and the reason is the correct explanation of assertion
B. If both assertion and reason are true and the reason is not the correct explanation of assertion
C. If assertion is false but reason is true
D. If assertion is true but the reason is false

Answer

To solve the question regarding the assertion and reason provided, we can break it down into a step-by-step analysis.

### Step 1: Understand the Assertion
The assertion states that "Among hydroxides of alkali metals, LiOH is the weakest base."
- **Explanation**: Hydroxides of alkali metals (LiOH, NaOH, KOH, etc.) are known to be basic. The strength of a base is often related to its ionic character. As we move down the group in the periodic table, the ionic character of hydroxides increases, leading to stronger bases.

### Step 2: Analyze the Reason
The reason given is "Among alkali metals, lithium has the highest ionization energy."
- **Explanation**: Ionization energy is the energy required to remove an electron from an atom. Lithium, being the smallest alkali metal, indeed has the highest ionization energy among its group. This is due to its small atomic size, which results in a strong attraction between the nucleus and the outermost electron.

### Step 3: Connect the Assertion and Reason
Now we need to determine if the reason provided correctly explains the assertion.
- **Connection**: While it is true that LiOH is the weakest base due to its covalent character (which is higher for Li due to its small size), the reason given (high ionization energy) does not directly explain why LiOH is the weakest base. The assertion is true, but the reason does not provide a correct explanation for it.

### Step 4: Conclusion
Based on the analysis:
- The assertion is true: LiOH is indeed the weakest base among alkali metal hydroxides.
- The reason is true: Lithium has the highest ionization energy among alkali metals.
- However, the reason does not correctly explain the assertion.

### Final Answer
The correct conclusion is that the assertion is true, the reason is true, but the reason is not the correct explanation for the assertion.