What happens inside a conductor when the current faces resistance? According to my book resistance depends on the the number of collisions free electrons suffer in any conducting device. Now insulators have no free electrons so how do they have high resistance like what collisions are taking place here? Am I getting resistance wrong or am I missing a point. Can someone explain this to me theoretically, numerically im aware of ohms law and how conductance and resistance are inversely related but what's the intuition behind it what is resistance as a whole?
 A: The electrical resistivity $\rho$ (a material property, distinct from the resistance, which is specific to the geometry) is the inverse of the conductivity $\sigma$.
The conductivity is modeled as $\sum_i e_in_i\mu_i$, which sums up terms related to the number $i$ of relevant charge carriers (e.g., electrons, holes, ions).
Each term is the product of the charge carrier charge $e$, charge carrier concentration $n$, and charge carrier mobility $\mu$. The mobility is the speed (specifically, the drift velocity obtained from a given driving force (such as an electric field) when encountering drag (such as scattering).
Insulators don't have a vast number of free electrons as metals do, but they do contain mobile charge carriers excited to the conduction band, for example, if by nothing else than the surrounding thermal energy.
Does this get at what you're asking about?
A: If you know Ohm's law, you know what resistance is: there is no other definition. How it's captured in a detailed model depends on the situation. The radiation resistance of an antenna has nothing to do with electrons. Free charge carriers can be holes or ions, not just electrons. An insulator has high resistance because it has few free charge carriers to carry a current.
A: I like to think of resistance more as the resistance of current flow. As my resistance becomes very large, less current will flow through my circuit.
You could even think about it with Ohm's law of course. Write it as a function of current vs resistance (I = V/R), if I have a circuit with a set voltage, I could add a resistor and I would get some current flow through my system, but if that resistance would be very large my current would be very low.
So in a insulator it would make sense why there's no free electrons (or barely any) is due to its high resistance of the material to conduct electricity.
You could imagine electrons flowing through a wire but the resistance would make it harder to get through the path. This image makes it very clear to understand.

