Step 1: Identify the context. The pupils enjoyed the Science exhibition (described as 'exciting') and did not want to leave — so the target word expresses a lack of desire to go. Step 2: Match meaning. Reluctant = not wanting to do something; unwilling = not willing to do something. Both convey lack of desire, fitting the context perfectly. Step 3: Eliminate distractors. Unable = cannot (implies inability, not reluctance). Afraid = fearful (implies fear, not desire to stay). Eager = keen to go (contradicts the sentence). Answer: unwilling.