Question

why gases are always in motion

Answer 1

Hi friend !
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there is negligible intermolecular force of attraction  between particles of gases and also the intermolecular space is very large two particles of gas state are very far from each other so they cant attract and are very far from each other s gas always flow and in motion.
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Answer 2

Gases are always in motion because it's molecules are held freely to move .The molecules of gases have a lot space between them so they can move freely.

Hope it help's U...!!!!