The interior surface of a neuron's plasma membrane at resting membrane potential will have a negative charge and contains less sodium than outside of the cell positive charge and contains more sodium than outside of the cell negative charge and contains more sodium than outside of the cell positive charge and contains less sodium than outside of the cell

The answer is 'negative charge and contains less sodium than outside of the cell'. This is called the resting potential. After depolarization, the ion channels open up and the intracellular sodium ions are pumped out of the neurons hence making the inside of the neurons electronegative compared to the extracellular matrix. The membrane potential is usually -70mV.

protons in

diagram is missing, but i will try to explain your doubt.

answer:

amplitude is the maximum displacement or distance moved on a point of a vibrating body or wave measured from its equilibrium position.it is equal to half the length of vibration path.