We use is/are and which to ask questions with one and ones.
• Is / Are = yes or no question
• Which = information question
• Is this one yours?
Yes, it is.
Yes, it is mine.
No, it isn’t.
• Are these ones yours?
Yes, they are.
No, they aren’t.
• Which one is yours?
This one is mine.
That one is mine.
• Which ones are yours?
Those ones are mine.
These ones are mine.