Final answer:
During an action potential, the neuron is refractory and cannot be excited by a second stimulus. Afterward, when the neuron is hyperpolarized, it requires stronger stimulation to fire another action potential.
Step-by-step explanation:
During the action potential, the neuron cannot be excited by a second stimulus; it is refractory. For a few milliseconds afterward, the hyperpolarized neuron is stronger, requiring a stronger stimulation than usual in order to fire. The correct answer to this question is b) Hyperpolarized; refractory; stronger.
During the absolute refractory period, another action potential cannot start due to the inactivation of voltage-gated Na+ channels. Once the channels are back to their resting conformation, the neuron can be excited by a new action potential, but it requires a stronger stimulus than usual because of the outflow of K+ ions, which makes it more difficult for the entering Na+ to depolarize the neuron.