What is the term for a type of reaction in which two substances react to produce a single compound?

When 2 substances react to produce a single compound it's called a SYNTHESIS reaction

Atomicity occurs to prevent updates of the database occurring only partially, which can cause greater problems than rejecting the whole series outright.some are monatomic, diatomic, triatomic etc because it shows the number of atoms. for example, monatomic means it contains only one atom.