Item 4:

As shown in the circuit, there is a potential difference across a resistor, if it is connected to a battery and a current is flowing.

Question :

Is there any difference in the physical state between the contact points A and B on the opposite sides of the resistor?

Which of the following answers do you think is correct or makes sense to you?

1) There is no difference in the physical state between the contact points
A and B.
2) There must be a difference, but I cannot say what it is.
3) Throughout the cross-section of the wires at A and B the density of the free electrons, forming the electric current, is different.
4) The surface of the wire at A and B is charged differently.
5) The free electrons at A and B, forming the electric current, have different energy.