Chlorine bleach can dissolve protein fibers, corrode metals, and discolor __________.

Chlorine bleach is known for its strong oxidative properties, which can lead to significant damage to many materials. In the context of the fibers listed in the options, silk is particularly vulnerable to chlorine bleach due to its protein structure. Bleach can cause discoloration in materials with protein fibers, such as silk, which is derived from natural sources.

While cotton is also a natural fiber and likewise could be impacted by bleach, it is typically more resistant to discoloration than protein fibers like silk. Nylon and polyester are synthetic fibers that do not have the same protein structure, which makes them less susceptible to the damaging effects of chlorine bleach. However, it is important to note that chlorine bleach can still discolor these synthetic fibers, depending on the formulation and concentration used.

The correct answer involves the need to recognize that chlorine bleach has significant effects on silk, leading to discoloration and degradation, far more than it would on cotton, nylon, or polyester. Because of its specific vulnerability, silk highlights the risks associated with using bleach on textiles and the importance of understanding fiber content during cleaning processes.