Concept:A discharge tube operates by reducing the gas inside it to lower the pressure, allowing electric current to pass through the gas.
Explanation:When most of the gas is pumped out of the discharge tube, the number of gas molecules inside decreases.
This reduction in gas molecules causes the pressure inside the tube to drop.
At low pressure, the remaining gas particles are far apart, so they can be easily ionised by the applied electric field.
Ionisation produces charged particles that conduct electricity through the tube.
Therefore, electricity is conducted at low pressure, not at high pressure or high voltage.
Answer:D. low pressure