Final answer:
An aluminum atom with a mass number of 27 and a proton number of 13 contains 14 neutrons.
Step-by-step explanation:
An aluminum atom with a mass number of 27 and a proton number of 13 contains 14 neutrons. The mass number of an atom is the sum of its protons and neutrons. To calculate the number of neutrons, subtract the number of protons (13) from the mass number (27). Therefore, 27 - 13 = 14 neutrons.