The process of joining many small molecules into larger molecules is called (1) neutralization (3) saponification (2) polymerization (4) substitution

(2) polymerization. polymerization is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks.

Answer: polymerization.

Justification:

Poly means many, and monomer means parts.

Then, a polymer is a compound made of many smaller molecules, and the process to form a polymer is named polymerization.

Polymers are large molecules formed by the combination of of many repeated units (monomers).

Some polymerization reaction are adition and condensation.

Some very well know polymers are polyethilene, nylon, pvc, polyester, among many other. They are also known as plastics.