My parents were confident of my success in the examination.

Answer: Option C

Confident : feeling or showing confidence in oneself or one's abilities or qualities.
Worried : anxious or troubled about actual or potential problems.
Pessimistic : tending to see the worst aspect of things or believe that the worst will happen.
Diffident : modest or shy because of a lack of self-confidence.
Depressed : (of a person) in a state of unhappiness or despondency.

Antonym of Confident is Diffident