1) Displacement reaction : The reaction in which an element displaces another element from a substance is called "displacement reaction." It is represented as
2) In displacement reaction one element displaces another element from its compound and takes its place therein.
3) Here in above equation hydrogen has displaced from acids by metals.
4) Double displacement : The reaction in which the constituent atoms of the reaction interchange by the decomposition of the two reactants, to produce new compounds are called double displacement reactions.
They are generally represented as follows.