Answer : The correct option is, Carbon-13
Explanation :
Isotope : It is defined as the element that have the same number of protons but have the different number of neutrons of each of the atom.
Atomic number is defined as the number of protons or number of electrons.
Atomic number of carbon = 6 = number of protons = number of electrons
Mass number is defined as the sum of number of protons and number of neutrons.
Number of neutrons = Mass number - Number of protons
For the given options:
1. Carbon - 7: Mass number = 7
Number of neutrons = 7 - 6 = 1
2. Carbon - 13: Mass number = 13
Number of neutrons = 13 - 6 = 7
3. Carbon - 6: Mass number = 6
Number of neutrons = 6 - 6 = 0
4. Carbon - 12: Mass number = 12
Number of neutrons = 12 - 6 = 6
Hence, the correct option is, Carbon-13