Naive or ingenuous (adj) - a naive or ingenuous person (noun)
naive because ingenuous means innocent and unsuspecting naive is asynonymfor ingenuous.
Sentence with the word ingenuous: He made an ingenuous admission to the teacher that he did not complete his homework as he had gone out with friends the previous evening.
The young man was inexperienced, trusting, naive and ingenuous.
Please review and edit the question; you do not want 'ingenuous', that is an adjective.
The word "ingenuous" would be used in a sentence like the word primitive. A example would be: "He told the truth because he was ingenuous." It can be also used for the phrase "ingenuous question".
Of honorable extraction; freeborn; noble; as, ingenuous blood of birth., Noble; generous; magnanimous; honorable; upright; high-minded; as, an ingenuous ardor or zeal., Free from reserve, disguise, equivocation, or dissimulation; open; frank; as, an ingenuous man; an ingenuous declaration, confession, etc., Ingenious.
He was not offended by her direct question because her manner was so ingenuous.
A good sentence using the word 'ingenuous' could be 'The student made an ingenuous remark by saying they forgot their homework on the bus'. Another sentence might be 'Sarah's ingenuous behavior made her easy prey for the robbery'.
She was getting tired of the child's constant need to ask ingenuous questions. The little girl was in fact ingenuous because she told the truth.
(not to be confused with ingenious, ingenuous means naive, frank, or candid)"In Billy Budd, Melville creates an innocent and ingenuous character.""New Orleans Saints fans have always appreciated the ingenuous nature of coach Sean Payton."