Blue colour of alkali and alkaline earth metals in liquid `NH_3` is due to

Options

A. ammoniated complex cation
B. ammoniated `e^-`
C. `d - d` transition
D. both (A) & (B)

Answer

To solve the question regarding the blue color of alkali and alkaline earth metals in liquid ammonia, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Context**: Alkali and alkaline earth metals dissolve in liquid ammonia and produce a blue-colored solution. This indicates that there is a specific reason for the blue color observed.

**Hint**: Consider what happens when metals react with ammonia.

2. **Reaction with Ammonia**: When alkali metals (like sodium, potassium) and alkaline earth metals (like calcium) react with liquid ammonia, they form ammoniated cations and electrons. The general reaction can be represented as:
\[ M + n \text{NH}_3 \rightarrow [M(NH_3)_n]^+ + e^- \]
where \( M \) is the metal, \( n \) is the number of ammonia molecules coordinated to the metal ion, and \( e^- \) represents the free electron.

**Hint**: Focus on the products formed from the reaction between the metal and ammonia.

3. **Formation of Ammoniated Electrons**: The blue color of the solution is primarily due to the presence of these ammoniated electrons. These electrons are solvated by ammonia molecules, which stabilizes them and allows them to absorb certain wavelengths of light, leading to the blue color.

**Hint**: Think about how the presence of free electrons can affect the color of a solution.

4. **Elimination of Incorrect Options**:
- **Ammoniated Complex Cation**: This is not the correct answer because the blue color is not due to the cation itself.
- **D-d Transition**: This is also incorrect because alkali and alkaline earth metals do not have d-orbitals in their electronic configuration.
- **Both A and B**: Since both options A and B are incorrect, this option is also not valid.

**Hint**: Analyze each option critically to determine its validity based on the chemical behavior of the metals in ammonia.

5. **Conclusion**: The correct answer is that the blue color of alkali and alkaline earth metals in liquid ammonia is due to the presence of ammoniated electrons.

**Final Answer**: The blue color is due to **ammoniated electrons**.