Answer the following question given this paragraph: 

As you learned in Chapter 1 "Introduction to Chemistry", the mass number is the sum of the numbers of protons and neutrons present in the nucleus of an atom. The mass number is an integer that is approximately equal to the numerical value of the atomic mass. Although the mass number is unitless, it is assigned units called atomic mass.


Q: What number is the sum of the numbers of protons and neutrons present in the nucleus of an atom?

 Choices:

- nuclear number

- combined number

- mass total

- mass number

A:
mass number
