Question

A metal X produces an oxide and nitride on burning in air, but does not liberate hydrogen with alkali. Another metal $Y$ produces an oxide and nitride on burning in air and also liberates hydrogen with alkalies. The metal $X$ and $Y$ respectively are:
(A) $Na,Mg$
(B) $Mg,Al$
(C) $Na,Al$
(D) $Al,Mg$

Answer 1

Due to the formation of an oxide film over the surface, alkaline earth metal elements are kinetically inert to oxygen and water and burns with dazzling brilliance in air. But p-block elements on heating in air forms trioxide and nitrides liberating hydrogen.

Complete step by step solution:
As we know that due to the formation of an oxide film over the surface, alkaline earth metal elements are kinetically inert to oxygen and water and burns with dazzling brilliance in air. But p-block elements on heating in air forms trioxide and nitrides liberating hydrogen.
Let us now take these alkaline earth metal and p- block metals into consideration, we know that when magnesium burns in air, it results in the formation of magnesium dioxide and magnesium nitride but it does not liberate hydrogen with alkali. We can represent this through the chemical equation:
$2Mg + {O_2} \to 2MgO \\\ \Rightarrow 3Mg + {N_2} \to M{g_3}{N_2} \\\$
Hence, the metal $X$is the Magnesium.
Now we also know that when aluminium is burnt in air,, it results into the formation of aluminium oxide and aluminium nitride which we can show using the chemical equation:
$4Al + 3{O_2} \to 2A{l_2}{O_3} \\\ \Rightarrow 2Al + {N_2} \to 2AlN \\\$
Aluminium when reacts with alkali it liberates hydrogen which we can show by the chemical equation as below:
$2Al + 2NaOH + 2{H_2}O \to 2NaAl{O_2} + 3{H_2}$
Therefore from the above explanation we can say that the metal $Y$ is Aluminium.
Sodium itself is an alkali metal hence it will not react with itself to liberate hydrogen thus it is incorrect and also the fourth option is wrong.

Hence, the correct answer is option (B).

Note: Aluminium is amphoteric in nature and therefore it can react with an acid as well as a base and when it reacts with a base the reaction is highly exothermic and thus liberation of a dihydrogen takes place and with acid it develops a protective layer of oxide.