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?

Answer: The mass number of an oxygen isotope that has nine neutrons is 17 and isotope is called as Oxygen-17.

Explanation:

Atomic number is defined as the number of protons or number of electrons that are present in an atom.

For a neutral atom:

Atomic number = Number of electrons = Number of proton

Atomic number = 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

Given: Number of neutrons = 9

Thus mass number = Number of protons + Number of neutrons = 8 + 9 = 17.

Isotopes are elements which have same atomic number but different mass number.

Thus the mass number of an oxygen isotope that has nine neutrons is 17 and isotope is called as Oxygen-17.