Protons: 53 Neutrons: 78
Work Step by Step
The atomic number, as shown by the periodic table, of Iodine is 53, meaning that there are 53 protons (the atomic number is the number of protons). Because it is Iodine-131, the atomic mass number of this isotope is 131 amu. Because both protons and neutrons weigh one amu while electrons are essentially weightless, this means that there must be 78 neutrons (53 protons+78 neutrons= 131 amu).