Erythematous gums, tongue allodynia (pain from light touch), and papillary atrophy of the tongue suggest a deficiency of which vitamin?

Erythematous, swollen, easily bleeding gingiva together with glossitis/papillary atrophy is the classic oral presentation of vitamin C deficiency (scurvy), reflecting impaired collagen synthesis. (Atrophic glossitis alone can also occur with B-vitamin or iron deficiency, but the prominent gingival findings described here point most specifically to vitamin C.)