Question

The alkali metals dissolve in liquid ammonia, it is found that

• A. The blue colour changes to bronze with increasing concentration
• B. Blue solutions are paramagnetic but bronze coloured solutions are diamagnetic
• C. Blue colour is due to the presence of solvated electrons
• D. All the facts given above are correct

Hint:

In liquid ammonia, alkali metals form solvated electrons, which lead to the characteristic blue colour, and this colour changes with concentration.

Answer 1

The Correct Option is D

Step 1: Alkali metals in liquid ammonia.
When alkali metals dissolve in liquid ammonia, they form blue solutions due to the presence of solvated electrons. The blue colour is a result of these solvated electrons being in an excited state. As the concentration of the alkali metal increases, the solution turns bronze due to the aggregation of solvated electrons.
Step 2: Paramagnetism and diamagnetism.
The blue solution is paramagnetic because of the unpaired solvated electrons, whereas the bronze solution becomes diamagnetic as the electrons pair up.
Step 3: Conclusion.
Therefore, all the facts given above are correct. The correct answer is (4) All the facts given above are correct.

Answer 2

This question checks whether each individual statement about alkali metal-ammonia solutions is chemically accurate, since the correct choice depends on all three sub-statements holding true together. Let's verify each option against the known behaviour of these solutions.

1. The blue colour changes to bronze with increasing concentration: At low concentration, alkali metals dissolved in liquid ammonia produce isolated, mobile solvated electrons trapped in cavities of ammonia molecules, giving the solution its characteristic deep blue colour. As the metal concentration rises past roughly 3 mole percent, these solvated electrons start to cluster and the electron pairs delocalize enough to create a state with metallic-like conductivity, changing the solution's appearance to a bronze or coppery, metallic sheen. This statement is factually correct.
2. Blue solutions are paramagnetic but bronze coloured solutions are diamagnetic: In the dilute blue solution, the solvated electrons remain largely unpaired, so the solution shows paramagnetic behaviour. In the concentrated bronze solution, the increased electron density allows electrons to pair up within clusters, and the solution behaves diamagnetically overall. This statement is also correct.
3. Blue colour is due to the presence of solvated electrons: This is the well-established explanation: the alkali metal ionizes in ammonia to give a metal cation and a free electron, and this electron becomes trapped and stabilized by surrounding ammonia molecules. The excitation of this trapped electron absorbs light in the visible region, producing the blue colour. This statement is correct as well.
4. All the facts given above are correct: Since options (1), (2), and (3) are each independently true, this option, which asserts that all of them hold, must be the correct choice.

Since each of the three individual statements about the colour change, magnetic behaviour, and origin of colour is independently verified to be true, none of them can be picked in isolation over the others.

Therefore, the correct answer is All the facts given above are correct.