Question

How is the mass number calculated for an element

Answer 1

The mass number of an element is equivalent to the number of Protons and Neutrons in the element. For example Oxygen has eight protons and neutrons, therefore its mass number is 16. You could also calculate this by simply rounding the atomic weight of the element to the nearest whole number. Oxygen's atomic weight is 15.994, which as you can see, would be rounded to 16 :)

Answer 2

The mass number of an element is equivalent to the number of Protons and Neutrons in the element.