On allowing ammonia solution of s-block metals to stand for a long time, blue colour becomes fade. The reason is:-

Options

A. Formation of `NH_(3)` gas
B. Formation of metal amide
C. Cluster formation of metal ions
D. Formation of metal nitrate

Answer

To solve the question regarding why the blue color of ammonia solution of s-block metals fades over time, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Initial Condition**:
- When s-block metals (like sodium, potassium, etc.) are dissolved in ammonia, they form a complex that imparts a blue color to the solution. This is due to the formation of a metal-ammonia complex.

2. **Observation of Color Change**:
- Over time, if the ammonia solution is allowed to stand, the blue color begins to fade. This indicates a change in the chemical composition of the solution.

3. **Identifying the Chemical Reaction**:
- The fading of the blue color can be attributed to the formation of metal amides. When s-block metals react with ammonia, they can form metal amides (MNH2) and hydrogen gas (H2).
- The general reaction can be represented as:
\[ \text{Metal} + \text{NH}_3 \rightarrow \text{MNH}_2 + \frac{1}{2} \text{H}_2 \]
- This reaction shows that the metal is reacting with ammonia to form a metal amide.

4. **Conclusion**:
- The formation of metal amides leads to the depletion of the metal-ammonia complex responsible for the blue color, thus causing the color to fade.

5. **Final Answer**:
- Therefore, the reason the blue color fades is due to the formation of metal amides.