Protons in a single atomic nucleus of a given element.
The mass number is the sum of the neutrons and protons which exist in the atomic nucleus of an isotope.
It usually represents the number 3 but it can also be used to represent other number's as well.
The atomic number is the number of protons in an element. Ex: Molybdenum's A.N. is 42. so it has 42 protons.
positive and negative