\[\mathbf{Pb}\left( \mathbf{S} \right)\text{ }+\text{ }\mathbf{CuSO4}\left( \mathbf{Aq} \right)\text{ }\to \text{ }\mathbf{PbSO4}\left( \mathbf{Aq} \right)\text{ }+\text{ }\mathbf{Cu}\left( \mathbf{S} \right)\]. The reaction is an example of ______ reaction.

Hint: The displacement reactions generally involve metal and a compound of a different metal so that a metal can displace a less reactive metal from the compounds which implies that only a higher reactive element in the compound with which it will react can replace the other element.

Complete answer:
A displacement reaction is the type of reaction in which the one atom or say a set of atoms gets displaced by another atom in the given molecule. Consider this as an example, when we add iron to a copper sulphate solution then it displaces the copper metal.
\[A\text{ }+\text{ }B-C\text{ }\to \text{ }A-C\text{ }+\text{ }B\]
In the above equation when A is more reactive than B in such a case A and B have to be either halogens where C indicates a cation or different metals wherein C indicates an anion.
A single displacement reaction which can even be called a single replacement reaction is defined as a type of oxidation-reduction chemical reaction when an ion or an element moves out from a compound that means one element is getting replaced by the other in a compound.
So basically the reactions in which the more reactive element displaces the less reactive element from its compound are popularly called as displacement reactions
\[Pb\left( S \right)\text{ }+\text{ }CuSO4\left( Aq \right)\text{ }\to \text{ }PbSO4\left( Aq \right)\text{ }+\text{ }Cu\left( S \right)\]
We can see clearly that the reaction of copper sulphate solution with lead is a type of displacement reaction. Here, the lead substitutes for the copper are getting precipitated out of solution because of insoluble lead (II) sulfate.

Note:
A double displacement reaction takes place when a part of two ionic compounds get exchanged which eventually results in making of two new components. These double displacement reactions mostly take place in aqueous solutions in which the ions precipitate and exchange of ions takes place.