As Earth revolves around the sun, what is this balance point that marks the actual center of revolution between two orbiting celestial bodies

center of mass

Explanation:

newton's law of gravitation is measured from the center of the mass, not the surface. so you will measure the radius from the center of the sun to the center of the earth.

an ion is a charged atom or molecule. it is charged because the number of electrons do not equal the number of protons in the atom or molecule. an atom can acquire a positive charge or a negative charge depending on whether the number of electrons in an atom is greater or less then the number of protons in the atom.