Question

When lead nitrate is heated, it is broken down into lead monoxide, nitrogen dioxide and oxygen as given below:
${\text{2Pb(N}}{{\text{O}}_{\text{3}}}{{\text{)}}_{\text{2}}} \to {\text{2PbO + 4N}}{{\text{O}}_{\text{2}}}{\text{ + }}{{\text{O}}_{\text{2}}}$
The above reaction is an example of:
A.Combination Reaction
B.Decomposition Reaction
C.Double decomposition Reaction
D.Displacement Reaction

Answer 1

Hint: A single substance on heating gives 3 products here. A single compound of lead on heating gives an oxide of lead, nitrogen dioxide and oxygen. The number of reactants in a combination reaction and displacement reaction should be 2 or more.

Complete step by step answer:
We aim to find the type of reaction.
Let us take option A. Combination reaction as the word suggests is the combination of 2 or more molecules to form a single compound. So, we can say that the given reaction is not a combination reaction.
Option B is a decomposition reaction in which one compound is decomposed to give 2 or more products. This means that one reactant is broken down on the action of heat into 2 or more products. As we observed, the equation mentioned above is thus a decomposition reaction.
${\text{XY}} \to {\text{X + Y}}$ Where XY is the parent molecule whereas X and Y are daughter molecules.
Option C is double decomposition. From the name, we can see that it is also a decomposition reaction. Here, the number of reactants should be 2 in which these two reactants interchange positive and negative ions between them.
The reaction mentioned above has only 1 reactant. So it is not a double decomposition reaction.
Option D is the displacement reaction in which there should be more than 1 reactant. The more reactive element replaces the less reactive element and forms the corresponding compound. In this type of reaction also we can see more than 1 reactant. So, this is not a displacement reaction. ${\text{X + Y - Z}} \to {\text{X - Z + Y}}$ If X is more reactive than Y.
Therefore, the answer can be found out by simply looking at the number of reactants in each type of reaction and comparing it with the given reaction.
Therefore, the correct answer is a decomposition reaction.
Thus, the correct option is (B).


Note:The decomposition reaction and double decomposition reaction are different. It is because decomposition involves only 1 reactant while double decomposition involves 2 or more. An example for double decomposition is ${\text{NaOH + HCl}} \to {\text{NaCl + }}{{\text{H}}_{\text{2}}}{\text{O}}$ . The positive and negative charges are interchanged. All other types of reaction except decomposition or thermal decomposition reaction have 2 or more than 2 reactants.