전혀
not at all, absolutely not
Meaning
전혀: with negation, “not at all,” “absolutely not.” In 전혀 몰라요, it completely negates knowing.
Why this form?
별로 — “not very / not particularly”: weakens the degree; 별로 몰라요 is closer to “I don’t know much,” less absolute than 전혀 몰라요.
아예 — “not at all / altogether / from the outset”: can also create total negation, but often adds a sense of complete exclusion or doing/not doing something from the start; 전혀 more directly marks zero degree.
하나도 — “not even one / not at all”: quantifies “not even one” and is very natural with countable items or colloquial emphasis; 전혀 is a more general degree adverb.
Natural usage
전혀 commonly combines with 모르다, 없다, 않다, 못하다: 전혀 모르다, 전혀 없다, 전혀 이해하지 못하다.
Forms not to confuse
별로
그 사람을 별로 잘 몰라요. — I don’t know that person very well.
아예
그 이야기는 아예 기억이 안 나요. — I do not remember that story at all.
하나도
무슨 말인지 하나도 모르겠어요. — I don’t understand a single thing you are saying.
Examples
우리가 누구인지도, 어떻게 여기 왔는지도 전혀 몰라요. — We have absolutely no idea who we are or how we got here.
저는 그 사실을 전혀 몰랐어요. — I did not know that at all.