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

When alkali metals dissolve in liquid ammonia, the metal atom loses its valence electron, giving a metal cation and a free electron. This electron does not stay free, it gets surrounded and stabilised by ammonia molecules, forming what is called a solvated electron.
Absorption of visible light by these trapped electrons is what produces the deep blue colour of a dilute solution, so the statement that blue colour comes from solvated electrons is accurate.
As more metal dissolves, the solvated electrons come closer together and start interacting, eventually clustering into paired states with metallic character, which is what turns the solution from blue to a bronze, metallic-looking solution.
Because the blue solution has predominantly unpaired electrons it is paramagnetic, while in the bronze solution the electrons pair up in clusters, making it diamagnetic. All three sub-statements describe genuine, independently documented aspects of this system, so none can be excluded.
Hence, the correct choice is the option stating that all the given facts are correct.

Answer 2

Rather than checking each statement in isolation, it helps to picture the alkali metal-ammonia system as concentration increases and see whether every part of the physical picture lines up with the given options.

1. The blue colour changes to bronze with increasing concentration: At the dilute end, individual electrons occupy solvent cavities and absorb visible light, appearing blue. As dissolution continues, the cavities begin to touch and overlap, electron density becomes continuous rather than localized, and the solution starts reflecting light like a metal surface, appearing bronze or coppery. This progression matches known experimental observation, so the statement holds.
2. Blue solutions are paramagnetic but bronze coloured solutions are diamagnetic: Magnetic behaviour follows directly from the electron picture just described. Isolated, unpaired solvated electrons in the dilute regime give net paramagnetism. Once electron density becomes continuous and electrons associate into paired, delocalized states in the concentrated regime, the magnetic moments cancel and diamagnetism dominates.
3. Blue colour is due to the presence of solvated electrons: This is the root cause underlying the entire picture above, the trapped, ammonia-stabilized electron is what absorbs visible radiation in the first place; without it there would be no colour change to describe at all.
4. All the facts given above are correct: Since the physical model of increasing metal concentration consistently explains the colour change, the magnetic behaviour, and the cause of the colour in one coherent picture, none of the three descriptive statements contradicts another.

Tracing the system from dilute to concentrated solution confirms that the colour change, the magnetic properties, and the cause of the blue colour are all correctly described.

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