The reaction in which two or more substance react with each other and form a single product is called combination reaction
It is a type of reaction where two or more reactants react to combine to give a single reaction.For example- water is added to quick lime to produce a lot of heat with the formation of calcium hydroxide or slacked lime

Combination reaction is a reaction in which two or more reactant react to form products. Ex:- H2+O2==H2O
Examples :* H2 +O2 gives H2O * H2 plus SO4 gives H2SO4
for ex : H2O+O2=2H2O
In those reaction two aur more element combine to form single substance are known as combination reaction