20. Which of the following statements are accurate?

A. Repolarization of a neuron results from potassium diffusing out of the cell.
B. At rest, excitable cells (e. g. neurons) have a negative charge.
C. Once a depolarization reaches threshold, an action potential will occur and can not be prevented.
D. To reach threshold, cells at rest must depolarize.
E. Sodium diffusing into a neuron will cause depolarization.

Statements A,C,D and E are correct

Statement B is wrong.

Explanation:

A. An efflux of extra potassium ion out of the cell leads to the cell being repolarized.

C. Once the threshold of depolarization reaches there much be an occurrence of action potential.

D. Depolarization of a cell at rest makes it reach it's threshold

E. Depolarization leads to the opening of the voltage-gated Na+ channels for Na+ influx.

the relative atomic mass of an element is the mass of one atom of that element, relative to 1/12th of the mass of a  1212c atom. to convert to an absolute mass in kg, it is necessary to multiply by  1.661×10−271.661×10−27.

the relative atomic mass is roughly equal to the number of neutrons, plus the number of protons, in the nucleus of the atom.

for elements with more than one stable isotope (different types of nucleus with different numbers of neutrons but the same number of protons), the quoted mass is usually the average mass, weighted by the relative abundance of the different isotopes.

multiply it by 5 in order for you to understand i cant give an exact answer.