Question

Gases begin to conduct electricity at low pressure because:
A: at low pressure gases turn to plasma.
B: colliding electrons can acquire higher kinetic energy due to increased mean free path leading to ionization of atoms.
C: atoms break up into electrons and protons.
D: the electrons in atoms can move freely at low pressure.

Answer 1

Hint: Any material will conduct electricity because of the presence of free electrons. Moving electrons transfer the electric energy from one end to the other. Materials which have loose bound electrons can conduct electricity easily as compared to the material which has tightly bound electrons.

Complete step by step answer:
In this question we have to tell why gases conduct electricity at low pressure. We know any substance will conduct electricity if it contains some free electrons or the material has enough free space for the movement of electrons. If the pressure is high then it means that gas molecules are tightly bound. Due to which the free path of electrons is low. This means electrons don't have enough path to accelerate, which means they can’t gain enough kinetic energy (as due to less path acceleration is low and enough velocity is not gained by electrons) needed for ionization of atoms. Due to which gases can’t conduct electricity at high pressure.
At low pressure molecules of gas are far from each other due to which gas molecules have enough mean free path to accelerate. This means gas particles will acquire enough velocity and hence kinetic energy for the ionization of other molecules. As the ionization of molecules will occur there will be free electrons as we know that free electrons conduct electricity. And this is why gases conduct electricity at low pressure.
So, the correct answer is option B that colliding electrons can acquire higher kinetic energy due to increased mean free path leading to ionization of atoms.

Note:
Pressure of gas should not be too low. If the pressure of the gas will be extremely low then gas molecules will be very far from each other. They will acquire high energy but the molecules will be so far that the collision will not be possible and hence ionization will not occur. Without ionization there will be no free electrons and if carriers are not present conduction will not take place.