Find the number of nitrates which gives NO2​ gas on heating from the following:
Nitrogen dioxide is released on heating:
$[N{H_4}N{O_3},\,KN{O_3},\,NaN{O_2},\,Pb{(N{O_3})_2},\,AgN{O_3}]$

Answer
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Hint: If a solution is heated and a brown gas emerges, the gas is nitrogen dioxide, which has a nitrogen component. The moist blue litmus paper turns red when exposed to this acidic gas. $N{O_2}$is the chemical symbol for nitrogen dioxide.

Complete Step-by-Step Explanation: In order to know that an acidic gas called nitrogen dioxide creates an acidic solution in water. It is one of the chemistry's more potently acidic gases. Nitric acid and nitrous acid are produced when it combines with water. $N{O_2}$ is the chemical symbol for nitrogen dioxide.
Now, let's examine the reaction that occurs when the compounds mentioned are heated. Lead monoxide, nitrogen dioxide, and oxygen gas are released when $Pb{(N{O_3})_2}$ decomposes under heat. Because of the presence of the nitrogen dioxide gas in which the gas evolved is in the reddish brown colour. Similarly, when$ZnS{O_4} \cdot 7{H_2}O$ is heated, deadly zinc oxide and sulphur oxide fumes are released, but no nitrogen dioxide gas is created. And the heat causes $NaHS{O_4}$ to transform into $N{a_2}S{O_4}$ together with water and oxygen. However, no gas other than ${N_2}O$ is evolved.
Therefore, two nitrates $Pb{(N{O_3})_2}$and $AgN{O_3}$resulting $N{O_2}$on heating,
$2Pb{(N{O_3})_2} \to 2PbO + 4N{O_2} + {O_2} \\$
 $2AgN{O_3} \to 2Ag + 2N{O_2} + {O_2} \\$
Note: It should be noted that when heated all of the nitrates that produce the nitrogen dioxide gas together with oxygen. Only a potassium and a sodium nitrate which break down to release an oxygen gas. $Pb{(N{O_3})_2}$is utilised in pyrotechnics like fireworks because heating it releases nitrogen dioxide.