Question

A metal is burnt in the air and the ash on the moistening smells \[N{H_3}\] . The metal is
A) \[{\text{Na}}\]
B) \[{\text{Fe}}\]
C) \[{\text{Mg}}\]
D) \[{\text{Al}}\]

Answer 1

Hint:We know that the Lithium in the respective group form nitride and from nitride ammonia can be formed. Now we have to find an element which is a diagonal relationship with lithium. So it will also form ammonia from the respective nitride.

Complete step by step answer:
The similarity between a pair of elements in different groups and different periods and located diagonally in the periodic table is called the diagonal relationship. On observation, it had been found that the elements of the second period have a striking similarity with the elements of the third period placed diagonally to each other, though belonging to different groups.
\[\begin{gathered}
  1\;\;\;\;\;\;\;2\;\;\;\;\;\;\;13\;\;\;\;14 \\
L{i_ \searrow }\;\;B{e_ \searrow }\;\;\;{B_ \searrow }\;\;\;C \\
  Na\;\;Mg\;\;\;Al\;\;\;\;Si \\
\end{gathered} \]
For example, lithium unlike other elements of the alkali metals (group 1) and beryllium like other elements of the alkaline earth metals (group 2), form compounds with significantly covalent character whereas other members of their respective groups form ionic compounds.
The behavior of lithium and beryllium is more similar to magnesium and aluminum respectively.
Similarities between Lithium and Magnesium are because of similar size, comparable atomic radii, and electronegativity.
Lithium and Magnesium both react slowly with water and their oxides and hydroxides are less soluble compared to the respective group element.
Only Lithium and Magnesium form nitride in their respective group (\[{\text{L}}{{\text{i}}_{\text{3}}}{\text{N}}\] and \[{\text{M}}{{\text{g}}_{\text{3}}}{{\text{N}}_{\text{2}}}\])
We can write the reaction of the process as:
\[3Mg + air \to M{g_2}{N_2} + MgO\]
Now the magnesium nitride prepared is subjected to moisture:
\[M{g_2}{N_2} + 6{H_2}O \to 3Mg{\left( {OH} \right)_2} + 2N{H_3}\]

Therefore, we can conclude that the correct answer to this question is option C.

Note:we know that nitride on reaction with water results in the formation of ammonia. So here we must try to find the element which first forms nitride with the reaction of air. We know that sodium, iron, and aluminum do not nitride on reaction with air.