Q: What is mass number?


Read this paragraph and choose the correct option from the provided answers:

All oxygen atoms have eight protons, and most have eight neutrons as well. What is the mass number of an oxygen isotope that has nine neutrons? What is the name of this isotope?.

 Choices:

- to total number of electrons and neutrons in a nucleus

- to total number of protons and electrons in a nucleus

- the total number of protons and chondrichthyes in a nucleus

- the total number of protons and neutrons in a nucleus


A:
the total number of protons and neutrons in a nucleus