Japanese grammar question?

Question:

1. In そうなんですか？　regarding the なん, is it because the そう　is regarded as a noun, so the ん becomes a なん?

2. 薬は？まだ飲んでない。Not sure what the "でない" is all about. I've only learned up to 飲まない。

3. ああ、顔色が悪いな。

今日は、帰ってもいいぞ。

can anyone explain what the end particles for both signify? What does "na? mean in the first sentence, and what does "zo" mean in the second sentence. I hear Japanese people say the latter a lot, like 行くぞ！！！

as always, thank you

Answer:

1. souna-no-desuka turns to "sounan desuka" it's a 'liaison'-like thing. (e.g. tell him = sounds like "tell'im") widely used for colloquial
e.g. "wakara-nai" --> "wakan-nai" (don't know), "shinji-rare-nai" --> "shinji-ran-nai" (can't believe it)

2. 飲んでない = have/has not taken (yet)
飲まなかった = didn't take, 飲まない = don't take

3. "na" "zo" are "sentence-ends" used in colloquial expressions to make it 'communicative', let's say..
there are more. "ne" "yo" "yone" "wa"
na" "zo" are both for male expression.