Elements on the periodic table are primarily arranged based on what two numbers?

Elements on the periodic table are primarily arranged based on their atomic number and mass number. The atomic number represents the number of protons in an atom's nucleus and determines the element's identity. This means that elements are organized in order of increasing atomic number from left to right across the periodic table.

The mass number, which is the sum of protons and neutrons in the nucleus, provides additional context about the types of isotopes and the distribution of those isotopes in nature. While the periodic table does not strictly arrange elements by mass number, it plays a significant role in understanding the physical properties and behaviors of the elements, including isotopes that may differ but are based on the same atomic number.

The other choices do not accurately reflect the primary basis of arrangement in the periodic table. For example, while atomic weight is involved in understanding the periodic trends, it is not the primary organizing principle compared to atomic number. Electron configuration is important for determining chemical behavior but is not used for the main arrangement of elements in the periodic table.