Question

A compound (X) gives brick red flame and breaks down on heating giving oxygen, brown gas (A) and (B). identify (X), (A) and (B) respectively.
A. $Ca{(N{O_3})_2},N{O_2},CaO$
B. $Ca{(N{O_3})_2},CaO,N{O_2}$
C. $Mg{(N{O_3})_2},MgO,N{O_2}$
D. $Mg{(N{O_3})_2},N{O_2},MgO$

Answer 1

The alkali metals and alkaline earth metal salts impart characteristic color to the flame. Brick red color is imparted by the element which has the atomic number 20.

Complete step by step answer:
Calcium is an alkaline earth metal and when it is put into a flame, it gives a brick red color, strontium gives crimson red color, barium gives apple green color and radian gives crimson color.
We can explain this, as alkaline earth metals or their compounds are put into a flame, the electrons absorb energy and they are excited to the higher levels. When they return to their ground state or normal state, the absorbed energy is emitted in the form of visible light of a particular wavelength. So, from the above, we can see that the compound of calcium will give a brick red color flame. So, it would be calcium nitrate.
Also, since magnesium and its compounds do not give flame tests. The gas evolved brown in color shows that it is the oxide of nitrogen. All these indicates towards the compound calcium nitrate
Calcium nitrate when heated gives calcium oxide (CaO), oxygen $({O_2})$ and $N{O_2}$. $N{O_2}$is a brown gas. $C{a^{2 + }}$ imparts brick red color or the flame.
The reaction is shown below:
$2Ca{(N{O_3})_2} \to 2CaO + {O_2} + 4N{O_2}$
So, (X) is $Ca{(N{O_3})_2}$
(A) is $N{O_2}$
(B) is CaO

Therefore, the correct answer is option (A).

Note: Magnesium atoms are smaller in size and their electrons are strongly held by the nucleus, so they will need a large amount of energy for the excitation of electrons to the higher energy which is not available in the Bunsen burner flame. So, they will not be able to impart color to the flame