What is a displacement reaction? Explain the statement ‘iron can displace copper from its salt solution, but copper cannot displace iron from its salt solution’.

Hint: The one which is more reactive will be able to displace the least reactive one from its salt solution. This chemical reactivity is linked based on its position in the reactivity series. Iron is placed above and the copper is placed below in the reactivity series.

Complete answer:
A displacement reaction is a type of reaction in which a more reactive metal will displace a less reactive metal from its compounds. These reactions are easily seen when a salt of the less reactive metal is in the solution. When the reaction occurs, the more reactive metal gradually disappears as it forms a solution, the less reactive metal coats the surface of the more reactive metal.
The above statement says iron can displace copper from its salt solution, but copper cannot displace iron from its salt solution, the reason for this statement being true is that iron metal is more reactive than copper. Because of this reason iron displaces copper from its salt solution whereas Cu being less reactive cannot displace iron from its salt solution.
If we assume copper sulphate as copper salt solution and iron sulphate as iron salt solution then the reaction can be written as:
$ Fe{\text{ }} + {\text{ }}CuS{O_4}\; \to FeS{O_4}\; + {\text{ }}Cu $
$ FeS{O_4}\; + {\text{ }}Cu\; \to no{\text{ }}reaction $
So we can see that iron is displacing copper from copper sulphate solution to form iron sulphate, but copper being less reactive is unable to displace iron from iron sulphate solution.

Note:
Chemical reactivity of metals is linked with their relative positions in the reactivity series. Certain metals can displace some metals from the aqueous solutions of their salts. A metal placed higher in the activity series can displace the metal that occupies a lower position from the aqueous solution of its salt. In the context of the above question, iron is placed above copper so it displaces copper from its salt solution.