7. the periodic table used today is arranged by increasing *
a. mass numbers
b. electrons in the nucleus
c. atomic numbers
d. charge

8. how many neutrons are there in an atom of phosphorus- 31? *
a. 14
b. 16
c. 31
d. 46

9. the average atomic mass for an element depends on *
a. the mass and percentage that exists of each naturally occurring isotope
b. the mass and number of protons of each artificial isotope
c. the mass and position of the electrons in each isotope
d. the average of the relative abundance of neutrons in all isotopes