Answer: C-13 isotope
Step-by-step 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
For carbon : number of protons = 6
number of neutrons = 7
Thus Atomic number = 6
Mass number = 7+ 6= 13
Thus isotope is called as carbon-13 isotope.