Step 1: Understanding moisture regain.
Moisture regain is the percentage of moisture a fibre absorbs from the atmosphere relative to its dry weight under standard conditions. It reflects the hygroscopic nature of fibres.
Step 2: Comparison of fibre moisture regain.
Different fibres absorb moisture differently based on their chemical structure. Natural protein fibres generally have higher moisture regain than synthetic fibres.
Step 3: Analysis of options.
(A) Cotton: Cotton has good moisture regain but is lower than that of wool.
(B) Wool: Correct — Wool has the highest moisture regain due to its protein structure and amorphous regions that attract water molecules.
(C) Polyester: Polyester is hydrophobic and has very low moisture regain.
(D) Nylon: Nylon absorbs some moisture but significantly less than wool.
Step 4: Conclusion.
Among the given fibres, wool absorbs the maximum moisture under standard atmospheric conditions.