My question is kinda simple (I hope).
When somebody asks you, for example:
学生りょうにＴＶがありますか。
Can you answer:
台所にはありますが、部屋にはありません。
Or do you use:
台所にありますが、部屋にはありません。
Can you also explain why that is, because I'm a little bit confused. Does the same thing happen with で->では, へ->へは?
Both work fine, but the focus of the answer would be different.
台所にありますが、部屋にはありません。
I think this answer would be more "direct". The question is "Is there a TV in the dorm?". A direct answer for this question would be "はい、テレビは台所にあります。", or simply "台所にあります。" with テレビ as the implied topic. After directly answering the question, 部屋にはありません follows, which is an optional piece of information.
台所にはありますが、部屋にはありません。
This answer sounds like you have already noticed that the questioner actually wants a TV in his personal room. By adding the contrastive-wa in the first half of the sentence, you signal that "there is a TV in the kitchen, but that's probably not what you want". As a consequence, (テレビは)部屋にはありません gets more focused.
More simply put, 台所にあります sufficiently works as a straight answer to the question, whereas 台所にはあります sounds like "Yes, there is, at least in the kitchen".
Note that those explicit は after 台所に/部屋に are all contrastive-wa. The implied topic is always テレビ(は) throughout the conversation. In different contexts, は directly after ～に can safely work as a topic marker. See: は、には、に。。。what is the difference between them?
