What is a polymer?

A polymer is defined as a large molecule composed of repeating structural units, typically linked together by covalent bonds. These structural units are called monomers, and when they chemically bond in large numbers, they form the vast array of polymers we encounter in nature and synthetic materials. Examples of polymers include natural substances like proteins and cellulose, as well as synthetic materials like plastics.

The other options do not accurately describe a polymer. A small molecule that forms during a chemical reaction refers to a different category of compounds that do not have the long, repeating structure characteristic of polymers. A type of solvent is unrelated to the structural definition of a polymer, as solvents facilitate solutions but do not comprise the chain-like structures that define polymers. Lastly, a bond formed between two atoms does not encapsulate the concept of polymers since this pertains to the interactions between atoms rather than the large, complex structures formed from many connected monomers.