what is the difference between combination reaction and decomposition reaction

A decomposition reaction is one where a compound is broken down into its constituent chemical species:
For example:2NaCl→2Na++Cl−2

The NaCl was broken down into the constituents Na+ and Cl−2

--(side note: the Cl is diatomic that explains the 2)Helpful 0
Confusing 0There are two types of replacement reactions, observe the differences:
Single Replacement: AB+C→AC+B

About Combination and Displacement reactions.