What is the difference between displacement and double displacement reactions?

Question.
What is the difference between displacement and double displacement reactions? Write equations for these reactions.

solution:
In a displacement reaction, a more reactive element replaces a less reactive element from a compound.

$\mathrm{A}+\mathrm{BX} \longrightarrow \mathrm{AX}+\mathrm{B} ;$ where $\mathrm{A}$ is more reactive

than B

In a double displacement reaction, two atoms or a group of atoms shift places to form new compounds.

$\mathrm{AB}+\mathrm{CD} \longrightarrow \mathrm{AD}+\mathrm{CB}$

For example, Displacement reaction

$\mathrm{CuSO}_{4}(\mathrm{aq})+\mathrm{Zn}(\mathrm{s}) \longrightarrow \mathrm{ZnSO}_{4}(\mathrm{aq})+\mathrm{Cu}(\mathrm{s})$

Double displacement reaction

$\mathrm{Na}_{2} \mathrm{SO}_{4}(\mathrm{aq})+\mathrm{BaCl}_{2}(\mathrm{aq}) \longrightarrow \mathrm{BaSO}_{4}(\mathrm{~s})+2 \mathrm{NaCl}(\mathrm{aq})$