Here are some synonyms for "naive":
* Innocent
* Unsophisticated
* Gullible
* Credulous
* Simple
* Unworldly
* Green (informal)
Example:
* "It was naive of her to believe that he would keep his promise."
* "The young man's naive optimism led him to believe that he could win the lottery."
Note: While "naive" can sometimes be used in a positive way to describe someone who is innocent and trusting, it more often carries a negative connotation, suggesting a lack of common sense or a vulnerability to being taken advantage of.