【How-to】How many protons and electrons does cadmium have

The chemical symbol for radon is Rn, and the mass number is usually placed either after the symbol (Rn-222) or to the left and above it (222Rn). In either case, it simply designates the element radon, which always has 86 protons, and that the particular isotope of radon in question is the one with 136 neutrons.