The correct option is A convinced
The word 'sceptical' refers to having doubts or reservations.
Option A, optimistic refers to being hopeful and confident about the future.
Option B, convinced refers to being completely certain about something.
Option C, credulous refers to the readiness to believe things.
Option D, hopeful refers to feeling or inspiring optimism about a future event.
Thus, according to the meaning, the word 'convinced' is the opposite of the word 'sceptical'.