The minister is optimistic about the new project just launched.

Answer: Option C

Optimistic : hopeful and confident about the future.
Stoical : enduring pain and hardship without showing one's feelings or complaining.
Dubious : hesitating or doubting.
Pessimistic : tending to see the worst aspect of things or believe that the worst will happen.
Cynical : believing that people are motivated purely by self-interest; distrustful of human sincerity or integrity.

Antonym of Optimistic is Pessimistic