When a gas is heated to become a plasma, the atoms (or the molecules) of the gas become ionised. In the ionisation, the atoms loose electrons from the exterior energy levels and thus heating to achieve a plasma will create free electrons and ionized atoms (or ionized molecules).
A plasma can not contain neutrons, because neutrons together with protons make the nuclei of the atoms. To free the neutrons from the atomn nuclei there would be necessary HUGE temperatures.
Also a plasma does not contain neutral elements (atoms) or (neutral) molecules, but Ionized atoms and/or molecules and free electrons.
Thus the good answer is d)
