"Is it true?"
What is the translation for 本当な if it can be very/really and used as the word true?
本当 is the noun and means "truth" or "real(ity)"
本当な is the adjective form and means "the true/proper/correct [following item]."
本当に is often translated as "really," but in the sense of "truly" rather than the sense of "very." In fact, "truly" is probably the more accurate translation.