b is not grammatically correct. You don't have "confidence of" anything. You have faith or confidence IN something.
You can also be confident OF something, but "confident" is not "confidence". One is an adjective, and one is a noun.
I am not confident of what I just said. I have no confidence in what I just said.
I am confident that Angela is a good teacher who understands the nuances of English grammar. I would put my faith in her, rather than Jeff. I wouldn't have confidence in Jeff, because I spotted several errors in his explanation. I am confident of being right about this because I have a lot of experience.
EDIT: Hmmm, I don't have much confidence of being right.
I think that statement is acceptable English, but you wouldn't see it often. It's an unusual way of speaking.
The key here is what follows your phrase. Is it a noun, or the -ing form of a verb?
I have confidence in Angela. I am confident of being right. I have no confidence of doing it well.
I'm really not happy about "confidence of -ing". Maybe someone else has an opinion. I'm pretty sure I would never use it.