Divide the planets based on their density, we call these groups

the 4 inner planets – those that are closest to the Sun – are all terrestrial planets,

Explanation:

the 4 outer planets are designated as gas giants

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.