The fluid outside a resting axon's membrane has mostly positively charged ________ ions.

A) serotonin
B) sodium
C) dopamine
D) protein

Positively Charged

A positively charged object has more protons than electrons, resulting in a net positive electric charge.

Sodium Ions

Positively charged atoms (cations) of sodium, crucial for various physiological processes including nerve impulse transmission and muscle contraction.

Serotonin

Serotonin is a neurotransmitter that has a key role in stabilizing mood, feelings of well-being, and happiness, as well as regulating sleep, digestion, and other bodily functions.