In the given nuclear equation, 222 86 Radon becomes 4 2 Helium plus blank. To determine the characteristics of the missing particle, we need to consider the conservation of both atomic number (Z) and mass number (A).
The atomic number (Z) represents the number of protons in an atom's nucleus. In the equation, the atomic number of the missing particle should be such that the sum of protons on the left side equals the sum of protons on the right side. Since Radon has an atomic number of 86 and Helium has an atomic number of 2, the missing particle must have an atomic number of 84.
The mass number (A) represents the total number of protons and neutrons in an atom's nucleus. Similarly, the mass number of the missing particle should be such that the sum of protons and neutrons on the left side equals the sum on the right side. Radon has a mass number of 222, and Helium has a mass number of 4. Therefore, the missing particle must have a mass number of 218.
Putting these values together, the characteristics of the missing particle are Z = 84 and A = 218. Therefore, the correct option is Z = 84, A = 218.