222 Rn 86
urgent |

The general representation of an element is

^{A}_{Z}X

where X is the symbol of the element, Z is its atomic number and A is its mass number. We are given that for radon, the atomic number is 86 and the mass number is 222. In a neutral atom

atomic number = number of protons = number of electrons

Thus, in radon, the number of protons and electrons is 86. Since

mass number = number of protons + number of neutrons

therefore, if 222 is the mass number, then number of neutrons = mass number - number of protons

= 222 - 86

= 136

**
**