Dilute solutions of alkali metals in liquid `NH_(3)` are blue. It is the ammoniated electron which is responsible for the blue colour of the solution, and the electrical conductivity is due to the ammoniated cation, `[M(NH_(3))_(x)]^(+)` as well as the ammoniated electrons, `[e(NH_(3))_(y)]^(-)`, values of x and y depend on the extent of solvation (by `NH_(3)`). Dilute solutions are paramagnetic due to free electrons.
What happens if alkali metals is allowed to react with concentrated liquid ammonia?

Options

A. Paramagnetic character of solvated electrons is retained
B. Solvated electrons associate to form electron-pairs and paramagnetic character decrease
C. Reducing character is increased
D. Reducing character is not affected

Answer

To answer the question regarding what happens when alkali metals react with concentrated liquid ammonia, we can break down the solution into a step-by-step explanation:

### Step-by-Step Solution:

1. **Understanding the Reaction**:
- When alkali metals (like sodium, potassium, etc.) are added to liquid ammonia, they initially form ammoniated cations and ammoniated electrons. In dilute solutions, these ammoniated electrons are responsible for the blue color and paramagnetic nature of the solution.

2. **Formation of Ammoniated Species**:
- In dilute ammonia, the alkali metal (M) reacts with ammonia (NH₃) to form the ammoniated cation \([M(NH₃)_x]^+\) and the ammoniated electron \([e(NH₃)_y]^-\). Here, \(x\) and \(y\) depend on the extent of solvation by ammonia.

3. **Behavior in Concentrated Ammonia**:
- When the concentration of ammonia increases, the behavior of the ammoniated electrons changes. The increased concentration leads to a higher likelihood of interactions between the electrons.

4. **Electron Association**:
- As the concentration of ammonia rises, the free ammoniated electrons tend to associate with one another, forming electron pairs. This association reduces the number of free electrons available in the solution.

5. **Change in Magnetic Properties**:
- Due to the formation of electron pairs, the paramagnetic nature of the solution decreases. In dilute solutions, the presence of unpaired electrons contributes to paramagnetism. However, when electrons pair up, the solution becomes more diamagnetic.

6. **Conclusion**:
- Therefore, when alkali metals react with concentrated liquid ammonia, the solvated electrons associate to form electron pairs, resulting in a decrease in paramagnetic character and an increase in diamagnetic character.

### Final Answer:
When alkali metals react with concentrated liquid ammonia, the solvated electrons associate to form electron pairs, which decreases the paramagnetic character of the solution.