the atomic number of an element is characteristic to that element. Atomic number is the number of protons of that element.
Mass number is the sum of protons and neutrons of the element.
since protons and neutrons have a mass of 1 unit each, they together make up the mass of the element.
atomic number - number of protons - 92
mass number - number of neutrons + protons = 234
number of neutrons = mass number - atomic number
neutrons = 234 - 92 = 142
answer is 142
