Vitamin deficiency diseases are a standard recall topic, and matching the symptom pattern to the responsible vitamin is the key skill. Vitamin C (ascorbic acid) is required for the synthesis and maintenance of collagen, the structural protein of connective tissue, gums, and blood-vessel walls. Its deficiency causes scurvy, whose hallmark symptoms are swollen and bleeding gums, loosening teeth, and impaired wound healing, exactly matching the described case and the classic affliction of sailors who lacked fresh fruit and vegetables. Therefore vitamin C deficiency is the correct cause. Vitamin D deficiency causes rickets, characterised by soft, deformed bones in children, not bleeding gums, so it is incorrect. Vitamin B12 deficiency leads to pernicious anaemia rather than the gum and wound symptoms described. Vitamin A deficiency causes night blindness and dryness of the eyes, which does not fit this clinical picture. This matches the NCERT table of vitamins and their deficiency diseases. As a plausibility check, the historical cure for scurvy was supplying citrus fruits rich in vitamin C, which directly confirms that the vitamin C link to bleeding gums and poor healing is the intended answer.