Which of the following s-block eleent reacts with `NaOH` to give water soluble complex:-

Options

A. `AI`
B. `Ca`
C. `Be`
D. `Li`

Answer

To determine which s-block element reacts with NaOH to give a water-soluble complex, we will analyze the properties of the given elements: aluminium, calcium, beryllium, and lithium.

### Step-by-Step Solution:

1. **Identify S-Block Elements**:
- S-block elements include Group 1 (alkali metals) and Group 2 (alkaline earth metals) of the periodic table.
- Aluminium is not an s-block element; it is a p-block element.

**Hint**: Remember that s-block elements are found in the first two groups of the periodic table.

2. **Evaluate Each Element**:
- **Lithium**: While lithium is an s-block element, it does not form a significant water-soluble complex with NaOH.
- **Calcium**: Calcium is an alkaline earth metal (Group 2) but does not form a stable water-soluble complex with NaOH.
- **Beryllium**: Beryllium, also an alkaline earth metal, is known to react with NaOH to form a soluble complex.

**Hint**: Consider the reactivity and solubility of the compounds formed when these elements react with NaOH.

3. **Reaction of Beryllium with NaOH**:
- Beryllium reacts with NaOH to form a soluble complex, specifically sodium beryllate (Na2[Be(OH)4]), which is soluble in water.
- The reaction can be represented as:
\[ \text{Be} + 2 \text{NaOH} + 2 \text{H}_2\text{O} \rightarrow \text{Na}_2[\text{Be(OH)}_4] + \text{H}_2(g) \]

**Hint**: Look for the formation of hydroxide complexes when metals react with strong bases like NaOH.

4. **Conclusion**:
- Among the given options, beryllium is the only s-block element that reacts with NaOH to form a water-soluble complex.

**Final Answer**: The correct answer is **Beryllium (option 3)**.