Here's why:

* Synthesis Reaction: A synthesis reaction is a type of chemical reaction where two or more reactants combine to form a single, more complex product.

* In this case: Sodium (Na) and chlorine (Cl) are the reactants, and they combine to form sodium chloride (NaCl), a single, more complex product.

This reaction is also a redox reaction. Sodium loses an electron (oxidation) and chlorine gains an electron (reduction).