Which explains why a gas does not have a fixed shape?

the particles have very high speeds.
the particles are not compressible.
the particles are charged.
the particles vibrate.

The particles have very high speeds.

Explanation:

the force between gas molecules is very weak so the molecules are very least bounded to each other.

Due to very less or weak interaction between the molecules the gas molecules can travel easily in the space.

Since the speed of gas molecules are random and the direction of motion is not influenced by the force between the molecules so here the gas can be compressed easily.

Due to this high speed of gas molecules they do not have a finite shape and it will obtain the shape of the container in which it is stored

So correct answer will be

The particles have very high speeds.