Which of the following is an example of a synthetic plastic?

Polyethylene is classified as a synthetic plastic because it is produced through chemical processes involving the polymerization of ethylene monomers, which are derived from petroleum. Unlike natural materials, synthetic plastics like polyethylene are manufactured deliberately to obtain desired physical and chemical properties. This allows for extensive usage in various applications such as packaging, containers, and insulation.

In contrast, amber is a fossilized tree resin and not a plastic, while natural rubber is harvested from rubber trees and represents a naturally occurring organic polymer. Shellac, a resin secreted by the lac bug, is also a natural product, used primarily as a finish in woodworking and as a food glaze. Thus, polyethylene is the clear example of a synthetic plastic among the given options.