# NEET Chemistry The s-Block Elements Questions Solved

Alkali metals dissolve in liquid ammonia to give a blue coloured solution which is due to the presence of-

(A) ${M}^{-}$atoms

(B) ${M}^{+}$ ions

(C) Solvated anions

(D) Solvated electrons

(D). The blue coloured solution of an alkali metal in ammonia is explained on the basis of formation of ammoniated (solvated) metal cations and ammoniated (solvated) electrons in the metal-ammonia solution in the following way :

$M\to {M}^{+}+{e}^{-}$

${M}^{+}+xN{H}_{3}\to {\left\{M{\left(N{H}_{3}\right)}_{x}\right\}}^{+}$

${e}^{-}+yN{H}_{3}\to {\left[e{\left(N{H}_{3}\right)}_{y}\right]}^{-}$

The blue colour of the solution is due to excitation of free electrons to higher energy levels. The absorption of photons takes place in the red region of the spectrum and hence, the solution appears blue in the transmitted light. As the concentration of the alkali metal increases, the metal ion cluster formation takes place and at very high concentration the solution becomes coloured like that of metallic copper.

Difficulty Level:

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