In which direction do particles in a solution move during passive transport

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.

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."