Which one of the following is NOT a natural fiber?

The correct option is Terylene.

To understand why Terylene is the correct answer, let's break down the classification of fibers into natural and synthetic categories:
1. Natural Fibers: These are fibers that are obtained directly from natural sources, such as plants and animals. Examples from the given options include:
- Jute: A natural vegetable fiber obtained from the stem of jute plants.
- Flax: A natural plant fiber obtained from the stem of the flax plant (used to make linen).
- Wool: A natural animal fiber obtained from the fleece of sheep, goats, or yaks.

2. Synthetic Fibers: These are man-made fibers synthesized in laboratories using chemical substances, primarily petrochemicals.
- Terylene: Terylene is a popular synthetic polyester fiber. It is produced by the polymerisation of ethylene glycol and terephthalic acid. Since it is chemically manufactured and not obtained from any plant or animal source, it is NOT a natural fiber.

Therefore, Terylene is the only option among the choices that is a synthetic fiber, making it the correct answer.