11. D
12.C
13. For 13 i would say B but not so sure
14. A
A substance cannot be a gas or a mixture. A pure<span> substance is something that occurs in nature. An element is made up of one type of atom only and cannot be split further. A compound has the combined properties of the elements from which it is made.
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Answeryou understand but id ont if your know the answer plz help me
Explanation:
B The collisions of the particles are elastic
