Question

Assertion: Alkali metals dissolves in liquid ammonia to give blue solution
Reason: Alkali metals in liquid ammonia give solvated species of the type (alkali metals).
(A) Both Assertion and Reason are correct and the Reason is the correct explanation of the Assertion.
(B) Both Assertion and Reason are correct but the Reason is not the correct explanation of the Assertion.
(C) The Assertion is correct but the Reason is incorrect.
(D) The Assertion is incorrect but the Reason is correct.

Answer 1

Hint: As we know that the alkali metals are the first family of the periodic table. These are having one electron in its outermost shell to which they can lose. As we go down the group in this family, the reducing character of the alkali metal increases.

Complete answer: or Complete step by step answer:
In solution, the alkali metal atom readily loses its valence electron. Both the cation and the electron combine with ammonia to form ammoniated cation \[{\left[ {{\rm{M(N}}{{\rm{H}}_{\rm{3}}}{{\rm{)}}_{\rm{n}}}} \right]^{\rm{ + }}}\]and ammoniated electron \[{\left[ {{\rm{e(N}}{{\rm{H}}_{\rm{3}}}{{\rm{)}}_{\rm{n}}}} \right]^{\rm{ - }}}\]as shown below.
\[{\rm{M + }}\left( {\rm{n}} \right){\rm{N}}{{\rm{H}}_{\rm{3}}} \to {\left[ {{\rm{M(N}}{{\rm{H}}_{\rm{3}}}{{\rm{)}}_{\rm{n}}}} \right]^{\rm{ + }}}{\rm{ + }}{\left[ {{\rm{e(N}}{{\rm{H}}_{\rm{3}}}{{\rm{)}}_{\rm{n}}}} \right]^{\rm{ - }}}\]
The ammoniated electron is responsible for the blue colour of the solution. The electrical conductivity of the solution is due to the ammoniated cation as well as ammoniated electron.
The dilute solutions are paramagnetic in nature because they contain free ammoniated electron. As the concentration increases, the ammoniated metal get bound by free electrons and thus the solution becomes bronze colour. The decrease in paramagnetic character suggests that in concentrated solution the ammoniated electrons associate to form electron pairs.
\[{\rm{2}}{{\rm{e}}^{\rm{ - }}}{{\rm{(N}}{{\rm{H}}_{\rm{3}}}{\rm{)}}_{\rm{n}}} \to {\left[ {{\rm{e(N}}{{\rm{H}}_{\rm{3}}}{{\rm{)}}_{\rm{n}}}} \right]_{\rm{2}}}\]
Therefore, we conclude that both statements are correct, but reason is not the correct explanation of assertion.

So, the correct answer is “Option B”.

Note:
The blue coloured solutions (less concentrated) are paramagnetic while bronze coloured solutions (high concentrated) are diamagnetic.