Which of the following is classified as a readily ignitable fiber?

Cotton is classified as a readily ignitable fiber due to its natural composition and structure. It is composed of cellulose, which is highly flammable, and when exposed to an open flame, cotton fabric will ignite quickly and burn at a relatively fast rate. This property makes cotton less safe in certain applications, especially in environments where there is a risk of fire.

In comparison, while silk is also a natural fiber that can ignite, it is more resilient to heat than cotton, making it slightly less readily ignitable. Nylon, a synthetic fiber, has a melting point and tends to melt rather than catch fire as easily as cotton. Polyester, another synthetic material, is generally more resistant to ignition due to its chemical structure, which does not support combustion as readily as cotton does. Thus, cotton stands out among the options provided as the most readily ignitable fiber.