Question

Why gases can fill the whole vessel in which they are enclosed?

Answer 1

Gases have low inter molecular force of attraction between the particles. So the particles are able to move randomly in all the directions at different speeds.
Hence they fill the whole vessel in which they are enclosed in

Hope This Helps You!

Answer 2

It is so because the molecules of a gas is held together by an almost negligible intermolecular attraction force , hence they(molecules) are able to move in any direction with random speed .
That's why they acquire the vessel wholely in which they are kept