Question: how many particles are there in the nucleus of a radon atom?
Answer: Iso- topes have the same number of protons (and therefore they are the same element), but they have different numbers of neutrons. For example, all radon isotopes have 86 protons (Z=86), but radon-222 has 136 neutrons (86 + 136 = 222), whereas radon-220 has only 134 neutrons (86 + 134 = 220).