What is the mass number of an oxygen atom with nine neutrons in its nucleus? (a) 8 (b) 9 (c) 17 (d) 16 (e) 18

Answer: mass number of oxygen is 17.

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.