The atomic mass number of an isotope is determined by the sum of its protons and neutrons. In this case, the atomic number is given as 5, which represents the number of protons in the nucleus of the atom. Since the isotope includes 6 neutrons, you simply add the number of protons (5) and neutrons (6) together to find the atomic mass number:
Atomic mass number = Number of protons + Number of neutrons Atomic mass number = 5 + 6 Atomic mass number = 11
Therefore, the atomic mass number of the given isotope is 11.