What is the arrangement of particles in a gas?
There is nothing I would call an arrangement for particles in a gas
The motion of molecules in a gas is a true example of what is known as "Brownian motion". This is a completely random movement of particles that exert very little (read "none" according to the kinetic-molecular theory of gases) force on one another.
This means, they move independently of one another in straight lines, and change direction in a totally random way upon collision.
So, if by arrangement, you mean any sort of regular pattern or structure, gas molecules show no arrangement at all.