Question

na+ ions are encouraged to move into neurons by
nonrandom assignment.
selective ion channels.
nonrandom movement.
the sodium - potassium pump.
electrostatic pressure.

Explanation:

Neurons have selective ion - channels that allow specific ions like $Na^+$ to pass through the cell membrane. The sodium - potassium pump actively transports $Na^+$ out of the neuron and $K^+$ into the neuron, but it's not what directly encourages $Na^+$ entry. Electrostatic pressure and non - random movement are not the main factors for $Na^+$ entry. Non - random assignment is a concept in research design, not related to ion movement in neurons.

Answer:

B. selective ion channels