β-keratin is

Answer: Option C

1. β-keratin is tough and insoluble.
- It is a fibrous structural protein found in the epidermal tissues of reptiles and birds.

2. It provides mechanical strength and water resistance.
- This property makes it suitable for forming scales, feathers, and claws.

3. β-keratin differs from α-keratin.
- While α-keratin is softer and more flexible, β-keratin is tougher and more rigid due to its unique structure.

4. Option C is correct as β-keratin is tough and insoluble, which aligns with its biological function.