Answer:
Atomic number or number of protons
Step-by-step explanation:
The given species are all isotopes of oxygen. Isotopes have the same number of protons or atomic number. They only differ in the number of neutrons.
- Isotopy is the existence of two or more atoms of the same elements having the same atomic number but different mass number.
- The different mass number is due to differences in their number of neutrons.
- Isotopes have the same electronic configuration and hence, they have the same chemical properties.
- Isotopes only differ in their masses.