Which of the following is an example of a common polymer?

A common polymer is a large molecule made up of repeating subunits called monomers. These macromolecules can be natural or synthetic and are pivotal in various materials and products we encounter daily. Plastic, a versatile and widely used material, is produced from synthetic polymers. Examples of plastics include polyethylene, polystyrene, and polyvinyl chloride (PVC), all of which are composed of long chains of polymerized monomers.

In contrast, water is a simple molecule made up of two hydrogen atoms and one oxygen atom, not a polymer. Salt (sodium chloride) consists of ionic compounds and does not have a polymeric structure. Alcohols, while they are organic compounds, are also not polymers as they are typically made up of smaller molecular units. Thus, plastic, identified as a common polymer, stands out as the correct answer due to its composition and usage in various applications within the beauty and nail technology industry, among others.