Which of the following ideas is not retained in the current theory of
atomic structure:
a. Most of the volume of an atom is empty space.
b. Electrons move around the nucleus as planets orbit the sun.
c. atoms have a central positively-charged nucleus

Hi again teatea!!

The correct answer is b. 

"Orbitals and orbits
When the a planet moves around the sun, you can plot a definite path
for it which is called an orbit. A simple view of the atom looks
similar and you may have pictured the electrons as orbiting around the
nucleus. The truth is different, and electrons in fact inhabit regions
of space known as orbitals."
From "chemguide.co.uk" site, for more info see this page:
http://www.chemguide.co.uk/atoms/properties/atomorbs.html

Search strategy:
orbitals electrons atom planet

Hope this helps. Please feel free to ask for a clarification if it is
needed.

Best regards.
livioflores-ga