Why do the nuclei of larger elements tend to be more unstable?

heavier atoms move slowly and get bombarded by more particles.

the positive charges of the many protons repel each other.

they have too many neutrons.

the electrons exert a destabilizing force on the nucleus.

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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all matter is made up of atoms

in any element all atoms are the same

elements in a compound are always in a constant ratio: apex