Answer: A famous scientist
Step-by-step explanation:
The following sentence is punctuated correctly:
"Charles Darwin, a famous scientist, lived in the nineteenth century."
The correct punctuation is to set off the descriptive phrase "a famous scientist" with commas on both sides to make it clear that this phrase is not essential to the meaning of the sentence. The commas indicate that "Charles Darwin" is sufficient to identify the person being referred to, and the descriptive phrase simply adds more information about him.