As an action potential occurs, the neuron's electrical charge changes from to a. negative; more negative b. positive; negative c. negative; positive d. positive; more positive

The correct answer is option C, that is, from negative to positive.  

Action potentials are those electrical impulses, which transmit signals around the body and are nothing more than a temporary shift, that is, from negative to positive in the neuron's membrane potential resulting due to the flowing of ions in and out of the neuron suddenly.  

During the resting state, that is, prior to an action potential, all of the gated potassium and sodium channels are closed. They open once an action potential has been initiated. The sodium channel opens and more sodium ions move within the cell, making the charge more positive.