"Is that a real rose?"
Translation:Ĉu tio estas vera rozo?
Because the point is not whether "that" semantically (by meaning) refers to a rose, but whether it grammatically (by position etc.) modifies the word "rozo" in that sentence.
In this case, it stands by itself grammatically; it's a pronoun. It is not "that rose" but simply "that", by itself.
And the demonstrative pronoun for objects is "tio".
Aaah, the importance of differentiating verda and vera ...
Oh, well, hopefully that made me memorise it.
Is vera correct here? Wouldn't reala be more appropriate? It is an actual rose, not a truthful one.
It is a genuine rose, not an existing one :)
vera is also Ne ŝajna, ne falsita, ne imitita, aŭtentika.
reala would insist that you're not just imaging it, or that it's a real-world one rather than an idealised perfect one.
Because esti is not a transitive verb that takes a direct object in the accusative case.
It's a linking verb or copula, linking a subject to a predicate -- and predicates like that are in the nominative case in Esperanto (no -n).