Final answer:
Subtracting the atomic number from the atomic mass of an element gives the number of neutrons in that atom, as the atomic number equals the number of protons, and the mass number is the total of protons and neutrons.
Step-by-step explanation:
When you subtract the atomic number from the atomic mass of an element, what you obtain is the number of neutrons in that atom. For example, in a chromium atom with mass number 52 and atomic number 24, the calculation would be 52 - 24, resulting in 28 neutrons. Each element has a distinct atomic number, equal to the number of protons it contains, while the mass number is the sum of protons and neutrons. Knowing the atomic number and mass number provides the information needed to determine the number of neutrons. The periodic table provides the atomic mass of each element, which is a weighted average of all naturally occurring isotopes and reflects the isotopic composition of the element on Earth.