On my request(1)/Amar introduced me(2)/to his friend, who is a singer(3)/and a scientist(4)/no error.(5)
Yes, if two nouns/adjectives are connected with and, as well as, etc for a single person then article is used only before 1st noun/adjective.
4. single person consists single article...
I thing and should be replaced with as well as
Frnd error hai isme.