Answer: mass number of oxygen is 17.
Step-by-step explanation:
Atomic number is defined as the number of protons or number of electrons that are present in an atom.
Atomic number = Number of electrons = Number of protons = 8
Mass number is defined as the sum of number of protons and neutrons that are present in an atom.
Mass number = Number of protons + Number of neutrons = 8+ 9 = 17
Hence, mass number of oxygen is 17.