Final answer:
The statement is True; opening channels for a cation with an equilibrium potential of -40 mV will cause depolarization, making the neuron more likely to fire an action potential and thus result in neuron excitation.
Step-by-step explanation:
If the equilibrium potential of a cation is -40 mV, then opening channels for this cation will result in excitation of the neuron. This statement is True because the equilibrium potential is the membrane potential where the net flow of the particular cation across the membrane is zero. For most neurons, the resting membrane potential is around -70 mV, so an equilibrium potential of -40 mV is more positive than the resting potential.
When channels specific to this cation open, the ions will move across the membrane in the direction that brings the membrane potential towards the equilibrium potential, in this case, making the inside of the neuron less negative (closer to zero). This movement toward a less negative internal environment is known as depolarization, which makes the neuron more likely to fire an action potential. Since action potentials are the means by which neurons send signals and excite other cells, opening channels for a cation with an equilibrium potential of -40 mV will indeed excite the neuron.