The only element with 78 protons is platinum (Pt).
Platinum is a metal element. Atomic mass of it is 195.08.
Platinum.
Each chemical element has a specific number of protons; the number of protons is equal to atomic number of the element.
The number of protons defines an element - the number of neutrons isn't needed to find the identity of the element. All ions and isotopes with 44 protons is ruthenium. However, with the information about the neutrons, we know the specific isotope: 101Ru.
Iodine is element number 53 and and so has 53 protons. There are thus 131-53 = 78 neutrons
The identity of an element is determined by the number of protons in the nuclei of its atoms. This is the atomic number of an element.
Experimentally, I'm not sure, but I know you can look at your periodic chart, the large number over the symbol of each element is teh number of protons in that element.
There are many different types of elements, all varying in the number of protons they contain. To determine the number of protons in a specific element, refer to the periodic table of elements. The atomic number (generally listed above the element's symbol, sometimes represented as 'Z') is equal to the number of protons in that atom.
By definition, the number of protons in the atoms of an element is the atomic number of the element.
Each element has a unique number of protons. If another atom has the same number of protons as that element, it is the same element.
The 131 number is the mass number: the sum of the number of protons and neutrons. Iodine has 53 protons and will have 53 electrons if its a neutral atom. To find the number of neutrons, just subtract the mass number with the number of protons 131 - 53 = 78 neutrons. See link below for periodic table.