The best answer to your question would be B:those who could not be broken down by physical means.
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. An example is Iron (III) , Iron (II) , lithium, and hydrogen.
When two carbon atoms are covalently bonded together, they try to achieve an octet structure so their electrons are 4 in number while each of them donates their remaining 2 so they end up sharing 4.