Learn Portuguese (Portugal): De quem é esta mochila?

Portuguese doesn't have a direct single-word translation for "whose" in questions. Instead, you literally ask "Of whom" using De quem. This structure is always used when asking about ownership.

Why do we use é here instead of está?

We use é, which comes from the verb ser (to be), because ownership is considered a permanent or defining characteristic of the object. You wouldn't use the verb estar, which is for temporary states or locations.

Why does the sentence use esta instead of este or essa?

Esta means "this" and is used because the object (mochila) is physically close to the speaker. It is feminine to match mochila. If the backpack were closer to the person you are talking to, you would use essa (that).

Can I change the word order to Esta mochila é de quem?

Yes, in spoken Portuguese, it is quite common to put the question words at the end. Esta mochila é de quem? is perfectly natural and means exactly the same thing. However, putting De quem at the beginning is the standard way to form the question.