Choice (a) is not correct because isotopes are atoms of the same element with different atomic weights due to a difference in neutron number whereas ions are charged particles created when atoms either lose or gain electrons. Choice (b) is also incorrect: the atomic weight of an atom is usually about double the atomic number because the atomic weight equals the number of protons (the atomic number) plus the number of neutrons.  From this explanation, you should be able to determine why answer (d) is also incorrect!