In what kind of reaction is a compound formed from two reactants

The kind of reaction depends. if you have only one reactant (element) and another element make one element, hen it is called synthesis. If you have 2 compounds react, then it is called a double replacement reaction. if it is only one compound and one element, then it is called a single replacement reaction. if the reaction has say CH4 + 2 O2 = = > CO2 + H2O, then it is called a combustion reaction.