Answer the following question:

Why should gases be insulators at ordinary pressures and start conducting at very low pressures?

At atmospheric/ ordinary pressures the Ions of gases move randomly and collide with each other , this random motion prevents it from setting a definite current in given direction, at low pressures these random motions decrease and if a potential difference is created between two points the gaseous Ions are able to move in definite direction setting a current. Hence, the gases become conductor at very low pressures.