How do I find the number of energy levels in a positive and a negative ion? And also how do I find the number of electrons in a ion and a atom?

Answer 1

The question is too general because the energy levels flip flop at certain points; however, here are some guidelines for a specific elements.
For the second part first.
For oxygen:
Look at the atomic number. The AN is 8; therefore, it has 8 protons and that means 8 electrons for the neutral atom (all atoms are neutral). If it is O^2- then it must have two electrons extra or 10 electrons total.

For energy levels in Oxygen:
The electron configuration for
8O is 1s2 2s2 2p4.
The 1s2 represent 2 electrons in an s energy level (technically 2 energy levels; 1 for each electron) but most call the s level one energy level.
Then there is the 2s energy level and the 2p energy level. If you talk about the O^2- ion then add two electrons to it and you have 1s2 2s2 2p6.