The correct answer is D. all of the above.
Ionization is the process of converting an atom or molecule into an ion by adding or removing an electron. In a circuit breaker, ionization is necessary to create a current path that will allow the breaker to open the circuit.
High temperature increases the rate of ionization by providing more energy to the atoms and molecules in the circuit breaker. This increased energy can cause the atoms and molecules to lose electrons, which creates ions.
Increased mean free path also increases the rate of ionization. The mean free path is the average distance that an electron travels before it collides with another atom or molecule. If the mean free path is increased, the electrons are more likely to collide with atoms and molecules that have a high enough energy to cause ionization.
Increasing field strength also increases the rate of ionization. The field strength is the strength of the electric field in the circuit breaker. If the field strength is increased, the electrons are more likely to be accelerated to a high enough energy to cause ionization.
Therefore, all of the above factors (high temperature, increase of mean free path, and increasing field strength) facilitate ionization in a circuit breaker.