usually 아니오(아뇨), 아니 is the answer for some question like would you like to play tennis? 테니스 칠래? no, I wouldn't. 아니오. 싫어요. Did you do your homework? 너 숙제 했어? no, I didn't. 아니오. 안 했어요. 아니오(아뇨), Anio 아니 ani 아니오(아뇨) and 아니 means same actually but usage is different. In korean, there are several ways for showing respect to other people who hear us out. And this means we do have several ways to speak to others with respect. We do speak different btw older people and younger people or formal and informal. For example, 아니오(아뇨) is more polite and showing more respect than 아니. we can't use 아니 for older people, cuz they feel offended and think the speaker is rude to say that. So when you want to be polite, you should use -오(요), -니다 ending words. 1. 아닙니다 2. 아니오 3. 아니 all of them means 'no' but 1st one is most polite and formal, but it's too formal for close older people, so if you want to be a bit lighter expression than that, you can say 2nd one. 3rd one is for btw friends who are similar age as you or younger than you. usually 안돼요 or 안돼 is the answer for the question which asks for allowance about something. 실험실에 들어가도 돼? Can I enter to lab? 안돼요. no, you can't 안돼요 Andwaeyo 안돼 Andwae 안돼요, 안돼 means same as well which is 'no(don't do or you are not allowed to do something)'. but it's just different way to express. 안돼요 is more polite and ok to use for older people or formal use. if you want to use more formal and clear and straight word, it could be 안됩니다. 안돼 is for casual usage btw friends or similar aged people or younger people. There are several way to show our respect when we use korean languages. even for similar aged people when you meet them for the first time, I would recommend use '-오(요), -니다' form. cuz when you are polite, it is always better. :) hope it could be the help. :)