"Whose oranges are these?"

You can say that too, "Чиї ці апельсини?", it will mean basically the same thing, just the grammar is different.

In English "this" and "these" work like both nouns or adjectives, but in other languages such as, for instance, German, Spanish and Ukrainian as well these concepts are different.

When you are talking about "this" as kind of an adjective (answering to "which?" basically) it will be цей-ця-це-ці, they describe a noun and cannot really stand on their own and take a verb.

When you are talking about "this" as not modifying a noun but being the subject of a sentence, it will be just це.

Це does not carry a gender and does not indicate singular/plural.

• Це апельсин. (This is an orange.)
• Це апельсини (These are oranges)

~~> These are sentences.

Цей-ця-це-ці carry a gender.

• Цей апельсин (this orange)
• Ці апельсини (these oranges)

~~> These are not sentences, just collocations, word combinations.