Step 1: Identify literal vs idiomatic meaning.
The phrase “to make clean breast of}” is not about cleaning or physical action. It is an idiom, and idioms often carry metaphorical meaning.
Step 2: Interpret the metaphor.
“Clean breast” metaphorically refers to revealing all that is hidden in one’s heart or mind—removing burdens by speaking the truth.
Step 3: Match with correct meaning.
Among the options, “To confess without reserve” captures the idea of making a complete and honest admission, aligning perfectly with the idiom’s accepted meaning. Other options like gaining prominence or praising oneself do not match the idiomatic sense.
\[
\boxed{\text{(c) To confess without reserve}}
\]