"Is that yours or mine?"
Translation:Ĉu tio estas via aŭ mia?
Use "tiu" when answering questions with "kiu" and use "tio" when answering questions with "kio." "Tiu" is like "that (one)" whereas "tio" is like "that (thing)."
Use tiu when accompanied by a name (tiu tranĉilo, tiu skribilo, tiu aŭto) and tio when it's just "that", without any specification.
It is not needed.
Yes. You mean is that mine or is that yours, or which is it, mine or yours.
I tried answering "Ĉu tio vias aŭ mias." and it was marked as incorrect. Why? Doesn't work with pronouns?
It's only adjectives that you can verb to get "to be [adjective]". Verbing nouns gets you "to use [noun]". I've never heard of verbing pronouns.
It's used for closed questions. "Is that yours or mine?" is closed because there are only 2 possible answers.
Open questions have their own question words (like who, what, where, which, etc.)