Within a discharge tube, electric conduction occurs due to the...

In a discharge tube, the gas is maintained at a very low pressure. When a high potential difference is applied across the electrodes, the gas atoms or molecules get ionized.

This ionization produces free electrons and positive ions.

The free electrons move towards the positive electrode (anode) and the positive ions move towards the negative electrode (cathode).

The simultaneous motion of these electrons and positive ions in opposite directions constitutes the electric current in the discharge tube.

Thus, electric conduction within a discharge tube occurs due to the motion of both electrons and positive ions.