Which of the following statements are true?
(i) Wool contains the protein keratin.
(ii) Wool contains sulphur.
(iii) Wool loses its strength when wet.
(iv) Alkali does not damage wool.

Question

Which of the following statements are true? 
(i) Wool contains the protein keratin. 
(ii) Wool contains sulphur. 
(iii) Wool loses its strength when wet. 
(iv) Alkali does not damage wool.

Accepted Answer

The correct option is 3:
The correct answer is Option 3, which includes statements (i), (ii), and (iii). The selection is correct because these three points accurately describe the fundamental chemical and physical properties of the wool fiber. Firstly, statement (i) is true: wool is classified as a natural protein fiber, and its molecular structure is predominantly composed of the fibrous protein called **keratin**. This keratin is responsible for wool’s unique characteristics like elasticity and resilience. Secondly, statement (ii) is also true: the keratin protein in wool contains amino acids, such as cysteine, which are rich in **sulphur**. These sulphur atoms link together to form strong **disulfide bonds**, which are the vital chemical cross-links that give wool its strength, stability, and characteristic crimp. Finally, statement (iii) is true due to the effect of moisture on the fiber's internal structure. When wool gets wet, water molecules penetrate the fiber and break the weaker internal **hydrogen bonds** that hold the protein chains together. This temporarily plasticizes the fiber, allowing the molecular chains to move more freely, which in turn leads to a significant reduction in its tensile strength, often losing up to one-third of its dry strength.

The incorrect option is 1:
This option incorrectly asserts that statements (i), (ii), (iii), **and (iv)** are all true. While the first three statements are chemically and physically correct, the inclusion of statement (iv), "Alkali does not damage wool," makes the entire option false. As a protein fiber, wool is extremely sensitive and vulnerable to strong alkaline substances. When exposed to a strong alkali, the chemicals attack and break down the crucial **peptide bonds** and **disulfide bonds** within the keratin structure. This process is known as hydrolysis. The chemical damage results in the yellowing of the fiber, a severe loss of strength, and ultimately, the complete dissolution of the wool. Therefore, any product with a high pH (alkaline) must be avoided when cleaning wool, making statement (iv) unequivocally false.

The incorrect option is 2:
This option suggests that (i), (iii), and (iv) are the true statements, thereby excluding statement (ii) and incorrectly including statement (iv). Statement (ii), "Wool contains sulphur," is a foundational truth about wool’s chemical makeup, as the sulphur-based **disulfide bonds** are the most distinctive and permanent structural feature of the fiber. Excluding this essential fact about its chemical composition renders the option incomplete. Moreover, this option repeats the error of including statement (iv), the scientifically inaccurate claim that alkali does not damage wool, when in reality, alkali severely degrades and dissolves this protein-based fiber.

The incorrect option is 4:
This selection proposes that (ii), (iii), and (iv) are true, incorrectly excluding statement (i) and including the false statement (iv). Statement (i), "Wool contains the protein keratin," is the most fundamental biological fact about wool. Keratin is the name of the protein that forms the entire structure of the fiber; to exclude this is to ignore the fiber's identity. Although (ii) and (iii) are correct on their own, the selection is flawed because it omits the primary constituent and includes the false assertion in (iv). It is vital for textile students to understand that the vulnerability of wool to alkali is directly tied to its protein (keratin) structure, making statement (iv) the key error in this combination.