Question

Which colour is developed to the solution when alkaline earth metals are dissolved in liquid ammonia?

• A. Crimson red
• B. Orange
• C. Deep blue black
• D. Faint green

Hint:

Differentiate between groups: Alkali metal solutions in liquid ammonia are initially deep blue (and turn bronze at very high concentrations). Alkaline earth metal solutions are uniquely deep blue-black.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
This is a theoretical factual question regarding the specific physical properties (coloration) of s-block elements when subjected to dissolution in anhydrous liquid ammonia.

Step 2: Detailed Explanation:
When group 1 (alkali metals) or group 2 (alkaline earth metals) are dissolved in liquid ammonia, they ionize and release their valence electrons into the solvent matrix.
These released electrons become surrounded by ammonia molecules, forming highly active species known as "ammoniated electrons" or "solvated electrons".
The generalized reaction for alkaline earth metals ($M$) is:
$M + (x+y)NH_3 \rightarrow [M(NH_3)_x]^{2+} + 2[e(NH_3)_y]^-$
The ammoniated electrons are solely responsible for strongly absorbing light in the visible spectrum.
While alkali metals (which release only 1 electron per atom) typically yield a striking deep blue color in dilute solutions, alkaline earth metals (which release 2 electrons per atom) generate a much higher electron density in the solution.
This higher concentration of solvated electrons causes alkaline earth metal solutions to appear intensely dark, specifically described chemically as a deep blue-black color.

Step 3: Final Answer:
The developed color is deep blue black, matching option (c).