"Is your one" VS "Yours is"

[Medio]

Hello everyone

I'm preparing for an exam that also includes an English test, and one of the preparation exercises asks to complete the following sentence:

"I know where my bag is, but I don't know where __________ "

The four possible options are as follow:

A) Is your.

B) Is your one. (Risposta Fornita - Errata)

C) Yours is. (Corretta)

D) Your is.

I chose (B), but it seems that according to the person who prepared this exercise the correct answer is (C).
I thought (B) is grammatically corect, while (C) is more like a slang. Is this the correct interpretation?

Thank you for your help

[Alan]

While 'your one' is (albeit colloquially) an acceptable substitute for 'yours', word order rules for implicit interrogatives in nominal clauses would require 'your one is' (not 'is your one').

Of the given choices, (C) is therefore the only possible answer.