What is the difference between an electrically neutral atom and an ion?

What is the difference between an electrically neutral atom and an ion?
  a. An ion has an unequal number of protons and electrons, while a neutral atom has an equal number.
  b. An ion has an equal number of protons and electrons, while an atom has an unequal number.
  c. An atom has an unequal number of neutrons and protons, while an ion has an equal number.
  d. An atom has its electrons in orbitals, while an ion has its electrons in its nucleus.
  e. An atom must have an equal number of neutrons and electrons, while an ion does not.

Question 2

Which atom would most likely be involved in an ionic bond?
  a. hydrogen
  b. oxygen
  c. sodium
  d. nitrogen
  e. helium