What is the process that forms large organic molecules?

Hint: Organic molecules are the compounds generally containing bonds between hydrogen and carbon. These molecules have the ability to combine together due to the presence of covalent bonds, which are formed by sharing of electrons. The smallest unit of a bigger organic molecule is known as a monomer.

Complete answer:
Organic molecules consist of hydrocarbons, and other molecules having nitro, carbonyl and other groups in the hydrocarbon chains. The property of the carbon atom to catenate, which is the ability to form long chains, gives rise to larger organic molecules.
The process that forms large organic molecules from a various number of smaller units of the organic species is called polymerization and the products formed from polymerization are called polymers. The polymerization is the result of smaller units combining called monomers. The word polymer itself suggests that ‘poly’ means ‘many’ and ‘mer’ means ‘units’. The monomers may attach at certain conditions of pressure and temperature to produce either chain, branched or cross linked polymers.
Example of polymerization is formation of polyethene or polyethylene from ethene. The reaction is,
$nC{{H}_{2}}=C{{H}_{2}}\xrightarrow{polymerization}{{(-C{{H}_{2}}-C{{H}_{2}}-)}_{n}}$
Hence, the process that forms large organic molecules is called polymerization.

Note:
Polymers are of various types like natural polymers – starch, cellulose, etc. semi synthetic polymers – rayon, synthetic polymers – Bakelite, polyethene. There are various types of polymerization like, addition polymerization in which monomers get added up. The other type is condensation polymerization where two molecules condense together and remove water molecules to form the polymer.