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 (NH₃), we can break it down into several steps:

### Step-by-Step Solution:

1. **Understanding the Context**: Alkali metals (Group 1) and alkaline earth metals (Group 2) have unique properties when they interact with liquid ammonia. When these metals dissolve in liquid ammonia, they form colored solutions.

**Hint**: Consider the properties of metals in solution and how they interact with solvents.

2. **Reaction with Liquid Ammonia**: When an alkali or alkaline earth metal (denoted as M) is added to liquid ammonia, it reacts to form a complex. The general reaction can be represented as:
\[ M + n \, NH_3 \rightarrow [M(NH_3)_n]^+ + e^- \]
Here, \( [M(NH_3)_n]^+ \) represents the ammoniated metal cation, and \( e^- \) is the ammoniated electron.

**Hint**: Think about how metals form complexes in solution and the role of ammonia as a ligand.

3. **Formation of Ammoniated Electrons**: The blue color observed in the solution is primarily due to the presence of these ammoniated electrons. These electrons are not bound to any specific atom and can move freely, contributing to the paramagnetic nature of the solution.

**Hint**: Recall that free electrons can absorb certain wavelengths of light, leading to color changes.

4. **Paramagnetism and Color**: The ammoniated electrons are responsible for the paramagnetic properties of the solution, which in turn leads to the characteristic blue color. The interaction of these electrons with light results in the absorption of specific wavelengths, which gives the solution its blue appearance.

**Hint**: Consider how color is related to electron transitions and the absorption of light.

5. **Conclusion**: Therefore, the blue color of alkali and alkaline earth metals in liquid ammonia is due to the presence of ammoniated electrons that make the solution paramagnetic.

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

### Summary of Key Points:
- The blue color arises from the formation of ammoniated electrons when alkali and alkaline earth metals dissolve in liquid ammonia.
- These electrons contribute to the paramagnetic nature of the solution, leading to the observed color.