Which of the following statements about atoms or ions is correct?
- AThe mass number of an atom is the total number of nucleons and protons.
- BThe electronic configuration of an aluminium ion, $\text{Al}^{3+}$, is 2,8,3.
- CHydrogen is the only atom that has an incomplete first electron shell.
- DMost of the volume of an atom is taken up by its nucleus.