Answer: The correct answer for the fill the blank is polymerization.
Polymerization is the process of formation of large molecule from the components of smaller repeating units. A chemical bond is formed between smaller units. The smaller repeating units are called as monomers and the giant molecule formed in this process is called as polymer.
Example- DNA ( deoxyribonucleic acid) is a giant molecule or polymer, which is formed by the joining of individual smaller units called as dNTP ( deoxyribonucleoside triphosphate). Thus, formation of DNA is a polymerization reaction.