In polymer chemistry, which of the following substances is an example of a natural polymer rather than a fully synthetic man-made polymer?

Introduction / Context:
Polymers are large molecules made up of repeating structural units called monomers. They can be classified into natural polymers, which occur in living organisms, and synthetic polymers, which are manufactured in chemical industries. Understanding this distinction helps in questions about materials used in daily life, such as plastics, fibres, and biomolecules. This question asks you to identify which listed substance is a natural polymer rather than a synthetic, man-made one.

Given Data / Assumptions:

• The options are Bakelite, Nylon, Polythene, and Starch.
• Bakelite is a well known synthetic thermosetting plastic.
• Nylon and polythene are classic synthetic polymers.
• Starch is a carbohydrate found in plants.
• We assume the standard classification used in basic polymer chemistry.

Concept / Approach:
Natural polymers are produced by living organisms. Examples include proteins (polypeptides), nucleic acids (DNA, RNA), cellulose, and starch. These biopolymers are synthesised through biological processes such as photosynthesis and metabolism. Synthetic polymers, in contrast, are produced by controlled chemical polymerisation of monomers in industrial settings, often derived from petroleum. Bakelite is a phenol-formaldehyde resin, nylon is a polyamide made from diamines and diacids, and polythene (polyethylene) is formed from ethene monomers; all are synthetic. Starch, however, is a natural polysaccharide made of glucose units and serves as an energy storage material in plants, making it a natural polymer.

Step-by-Step Solution:
Step 1: Identify which substances are clearly synthetic plastics. Bakelite is a thermosetting plastic used in electrical fittings and handles. Nylon is a synthetic fibre used in textiles, ropes, and plastics. Polythene is a synthetic plastic used in bags, bottles, and containers. Step 2: Consider starch. Starch is a carbohydrate stored in plant tissues such as potatoes, rice, and wheat grains. Step 3: Recall that starch consists of many glucose units joined together, forming a long chain polymer. Step 4: Conclude that starch is the only natural polymer among the options.

Verification / Alternative check:
Biology and chemistry textbooks describe starch as a polysaccharide composed of alpha glucose units linked through glycosidic bonds, forming amylose and amylopectin chains. It is synthesised in plants by enzymes and is not produced in chemical factories. On the other hand, the manufacturing processes for Bakelite, nylon, and polythene are classic examples of synthetic polymerisation reactions taught in industrial chemistry chapters. These reactions use monomers derived from petrochemicals or simple organic reagents and are controlled in reactors, confirming their synthetic nature. This clear difference confirms that starch is the natural polymer in the list.

Why Other Options Are Wrong (synthetic polymers):
Option A (Bakelite): A synthetic thermosetting resin formed by condensation of phenol and formaldehyde; not natural. Option B (Nylon): A synthetic polyamide made by condensation polymerisation of diamines and dicarboxylic acids or related monomers. Option C (Polythene): A synthetic addition polymer formed from ethene monomers; a widely used plastic.

Common Pitfalls:
Students sometimes assume that anything used in everyday objects like food packaging or clothing must be synthetic, and they may forget that starch is a natural carbohydrate. Another confusion arises because the word “polymer” is often associated with plastics, leading to the wrong belief that only industrial materials are polymers. To avoid these mistakes, remember that many biological macromolecules, including starch, cellulose, proteins, and DNA, are natural polymers built from repeating monomer units.

Final Answer:
The natural polymer among the given options is Starch.