Vitamin C (ascorbic acid) deficiency causes scurvy, characterized by fatigue, swollen gums, bleeding from mucous membranes, and poor wound healing. Scurvy was historically common among sailors on long voyages without fresh fruit. Vitamin C is essential for collagen synthesis. The other options are unrelated: Haemophilia is a clotting disorder, colour blindness is genetic, and loss of appetite is nonspecific.