A __________ thread made of synthetic fibre is actually stronger than a steel wire of the same thickness.

Introduction:
This question tests basic knowledge of materials, specifically the comparative strength of synthetic fibres and metals. It is a popular science fact often mentioned in school textbooks that highlights how strong certain man made fibres can be when compared with traditional natural materials and even metals of the same thickness.

Given Data / Assumptions:

• A particular synthetic fibre thread is known to be stronger than a steel wire of the same thickness.
• The options list common fibres such as wool, cotton, jute, nylon, and silk.
• We assume that the comparison is for equal thickness and under similar testing conditions.

Concept / Approach:
Synthetic polymers such as nylon have very high tensile strength because of their long chain molecules and strong intermolecular forces. When drawn into fine fibres, nylon can withstand significant pulling force before breaking. For the same thickness, a nylon fibre can carry more load than a steel wire. Natural fibres like wool, cotton, jute, and silk are strong for textile use but do not match nylon in strength for equal diameter comparison.

Step-by-Step Solution:
Step 1: Recall that synthetic fibres such as nylon and polyester are known for high tensile strength.Step 2: The statement that a thread is stronger than a steel wire of the same thickness is a standard textbook example for nylon.Step 3: Natural fibres like wool, cotton, jute, and silk are comparatively weaker and more easily break under high tensile load.Step 4: Therefore, the blank must be filled with the name of the synthetic fibre nylon.Step 5: Choose nylon from the options as the correct answer.

Verification / Alternative check:
If you have seen experiments or demonstrations, a fine nylon fishing line or nylon thread can carry surprising weights without breaking, while a steel wire of equal thickness can snap earlier. This supports the statement. In industry, very strong ropes and safety belts are often made of synthetic fibres like nylon, not of cotton or jute, which further confirms the concept.

Why Other Options Are Wrong:
Wool is a natural animal fibre used mainly for warm clothing and has lower tensile strength than nylon. Cotton is a plant fibre valued for comfort but is not as strong as nylon at the same thickness. Jute is a coarse plant fibre used for bags and ropes but still weaker than nylon thread in strength to thickness comparison. Silk is strong among natural fibres but does not surpass nylon in this standard example.

Common Pitfalls:
Students may think of silk because it is marketed as strong and luxurious, or of jute because it is used in ropes. However, the specific textbook comparison with steel wire refers to nylon. Another mistake is to ignore the condition that thickness is the same; if thickness differs, strength comparisons can change, but the question clearly assumes equal thickness.

Final Answer:
Correct option: Nylon