Question

Nitrogen cannot be obtained by heating
(A) $Ba{({N_3})_2}$
(B) $Pb{(N{O_3})_2}$
(C) ${(N{H_4})_2}C{r_2}{O_7}_{(s)}$
(D) $N{H_4}N{O_{2(s)}}$

Answer 1

Alkali metal nitrates except lithium decompose upon strong heating to give oxygen gas and alkali metal nitrate. Now decompose all four compounds with this information, try and solve the given question.

Complete answer:
This is based on the properties of inorganic compounds and their corresponding nitrates. Now decompose and break down all these four compounds through decomposition reaction.
Let us start with,
Thermal decomposition of Barium azide, $Ba{({N_3})_2}$ :
$Ba{({N_3})_2}\xrightarrow{\Delta }Ba + 3{N_2} \uparrow$
So from above thermal decomposition reaction it was clearly observed that after the thermal decomposition of barium azide, nitrogen is obtained along with nitrogen we get Barium.
Now, let us consider thermal decomposition of ammonium nitrate $N{H_4}N{O_{2(s)}}$
$N{H_4}N{O_{2(s)}}\xrightarrow{\Delta }{N_2} \uparrow + 2{H_2}O$
So from above thermal decomposition reaction it was clearly observed that after the thermal decomposition of ammonium nitrate nitrogen is obtained along with water vapour.
Now, let us consider thermal decomposition of ammonium dichromate ${(N{H_4})_2}C{r_2}{O_7}_{(s)}$
${(N{H_4})_2}C{r_2}{O_7}_{(s)}\xrightarrow{\Delta }{N_2} \uparrow + C{r_2}{O_3} + {H_2}O$
So from above thermal decomposition reaction it was clearly observed that after the thermal decomposition of ammonium dichromate gives nitrogen along with water vapour and solid chromium oxide.
Similarly let us consider thermal decomposition of lead nitrate $Pb{(N{O_3})_2}$
$2Pb{(N{O_3})_2}_{(s)}\xrightarrow{\Delta }2PbO + 4N{O_2} + {O_2}$
So from above thermal decomposition reaction it was clearly observed that after the thermal decomposition of lead nitrate gives nitrogen dioxide along with formation of lead dioxide (white precipitate) and oxygen gas which is immediately released into the atmosphere.
So, from the above decomposition reaction and observation it was clear that the thermal decomposition of lead nitrate $Pb{(N{O_3})_2}$ cannot give nitrogen.

So, the correct answer is, Option B.

Note: Thermal decomposition reaction is the reaction in which compounds break down into two or more products from one reactant. Colour change is observed during this reactions; some thermal decomposition reactions are reversible.