The correct option is 20Ne.
The 19F given in the question is an atom of fluorine. It has 9 electrons, 9 protons and 10 neutrons. Note that, for a neutral atom, the number of electron and proton are always the same. The number, 19 at the back of fluorine symbol represent the mass number, which can be obtained by adding the proton number and the neutron number. Thus, 10 + 9 = 19. From the options given above, it is only Ne that has 10 neutrons.
