Question

why does a gas fill a vessel completely

Answer 1

here is ur answer.
hope it helps....

Answer 2

Hey Mate! Here's ur answer.
Gases have the least Intermolecular Force of Attraction & most Intermolecular Space so, it follows the property of Fluidity. So gases takes up the shape or fills the vessel completely, whereas Water also being fluid changes the shape but the volume is same.

I Hope It Helps.....☺️
# Yash