The atomic mass number of an isotope is the sum of the number of protons and neutrons in the nucleus of an atom. Given that the atomic number is 5 (which represents the number of protons), and the isotope includes 6 neutrons, we can calculate the atomic mass number as follows:
Atomic mass number = Atomic number + Number of neutrons Atomic mass number = 5 + 6 Atomic mass number = 11
Therefore, the isotope with an atomic number 5 and 6 neutrons has an atomic mass number of 11.