vitamin B2 vs vitamin B

vitamin B2 and vitamin B both are nouns.

Word	Noun	Adjective	Verb	Adverb
vitamin B2	Yes	No	No	No
vitamin B	Yes	No	No	No

As nouns, vitamin B is a hypernym of vitamin B2; that is, vitamin B is a word with a broader meaning than vitamin B2:

vitamin B2: a B vitamin that prevents skin lesions and weight loss
vitamin B: originally thought to be a single vitamin but now separated into several B vitamins

Other hypernyms of vitamin B2 include B-complex vitamin, B, B complex, B vitamin, vitamin B complex.

vitamin B2 (noun)	vitamin B (noun)
a B vitamin that prevents skin lesions and weight loss	originally thought to be a single vitamin but now separated into several B vitamins