Answer: B. 15
Explanation:
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
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
Given : number of protons = 8
number of electrons = 8
number of neutrons = 7
Hence, mass number = Number of protons + Number of neutrons = 8+ 7 = 15.
