What does this model most likely represent?

a model is a representation of an idea, an object or even a process or a system that is used to describe and explain phenomena that cannot be experienced directly

option a is correct i.e.

explanation:

in context to the membrane of nerve impulse, the outer membrane of neuron is semi permeable that is only sodium ions can pass through the membrane i.e. smaller ions can pass through the membrane while larger ions cannot pass through it.

true is the