What energy level is in the element colbalt in

Which of these best describes an ionic bond?

Which of the following observations indicates that there is a small, dense, positively charged part in the center of an atom? some uncharged particles are scattered by a gold foil. all uncharged particles are attracted towards a gold foil. all positively charged particles pass straight through a gold foil. some positively charged particles bounce back from a gold foil.

The number to the right of an element's symbol (ex. c-12) identifies the of an isotope.