Which of the following is not a polymer?
Correct option is D. Fat
Wool consists of protein together with a small percentage of lipids.Proteins are polymers made out of amino acids. Hence, wool is a polymer.
Cotton is composed of pure cellulose, a naturally occurring polymer. Cellulose is a carbohydrate, and the molecule is a long chain of glucose (sugar) molecules.
Leather is made from animal skin, rawhide and animal skin is made of a polymer called collagen.
Fat molecules are made up of four parts, a molecule of glycerol and three molecules of fatty acids. Most fats are glycerides, particularly triglycerides (triesters of glycerol). Hence, not a polymer.
Hence, option $$D$$ is the answer.