Black vs Negro

Black and Negro both are nouns.

Word	Noun	Adjective	Verb	Adverb
Black	Yes	No	No	No
Negro	Yes	No	No	No

As nouns, Black and Negro are synonyms defined as:

Black and Negro: a person with African ancestry, "Negro" and "Negroid" are archaic and pejorative today

Other synonyms of Black include African-American, Negroid.

Black (noun)	Negro (noun)
a person with African ancestry, "Negro" and "Negroid" are archaic and pejorative today	a person with African ancestry, "Negro" and "Negroid" are archaic and pejorative today
popular child actress of the 1930's (born in 1928)
British chemist who identified carbon dioxide and who formulated the concepts of specific heat and latent heat (1728-1799)