Acomposition reaction(sometimes also called acombination reactionor asynthesis reaction) produces a single substance from multiple reactants. A single substance as a product is the key characteristic of the composition reaction. There may be a coefficient other than one for the substance, but if the reaction has only a single substance as a product, it can be called a composition reaction. In the reaction

2 H2(g) +O2(g) →2 H2O(ℓ)

Adecomposition reactionstarts from a single substance and produces more than one substance; that is, it decomposes. One substance as a reactant and more than one substance as the products is the key characteristic of a decomposition reaction. For example, in the decomposition of sodium hydrogen carbonate (also known as sodium bicarbonate),

2 NaHCO3(s) →Na2CO3(s) +CO2(g) +H2O(ℓ

3.Displacement Reaction:

Reactions in which the more reactive element displaces the less reactive element from its compound are called displacement reactions.

Zinc displaces copper in copper sulphate to form zinc sulphate.

Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)