1. 알았어 and 알았지 are about the same in meaning but differ slightly in certain contexts. - In firm statements, only 알았어 is used widely as an acknowledgment that one understood something, like "I got it". - 알았지 in non-question form has a tone of talking to oneself, so it is mostly used in literature and song lyrics. - In questions, both are commonly used to make sure the other side understood something("Did you get it?"). 2. -야 and -에요 are two of the sentence ending forms of the verb 이다. Here are the four basic sentence ending forms. - 입니다 (formal and polite) - addressing a group of people, as with TV, radio broadcasts. - 이다 (formal and casual) - used in dry materials, like textbooks, dissertations, literature, etc. - 이에요, 예요 (informal and polite) - between adults in most everyday situations. - 이야, 야 (informal and casual) - when speaking with someone close to you or children. 에에요 comes after a 받침(bottom consonant), and 예요 after a no-받침 syllable: 여기가 우리 집이에요. 여기가 우리 학교예요. Same principle goes for 이야 and 야: 저기는 은행이야. 저곳은 교회야. 3. -는데 and -면 are verb connective forms which are always neutral. Honorifics and polite forms (which are two different concepts) only apply to verb stems (가다 vs 가시다), sentence endings (가 vs 가요, 간다 vs 갑니다), or some special nouns (진지 vs 밥). * -는데: connects two clauses with a loose contradiction or contrast, or other vague relationship. * -면: connects clauses or phrases with a direct condition, like "if A then B" (A면 B이다). Examples: - 해가 나왔는데 한쪽에선 비가 온다: The sun's out but it's still raining on one side. - 그 약 많이 먹으면 위험해: If you take too much of that medicine, it'll be dangerous.

1. 알았어 means, I know it 알았지 + question mark(?) means, do you understand? 알았지 + (.) means, short term version of a sentense '알고있었지'. That means'I already knew it' 2. The difference of those setense, The later one have meaning respect or formal. For example, A sentence 'what's up?' is used only friendly or not elder people. To that people, you will say 'how are you?'. It seems like that. 3. Sorry, this is hard to say.