Which number determines the arrangement of elements in the modern periodic table?

• A. Atomic mass
• B. Number of neutrons
• C. Atomic number
• D. Mass number

Answer: (C)

Verified step by step guidance

1. Understand that the modern periodic table arranges elements based on a fundamental property of atoms.
2. Recall that the atomic number represents the number of protons in the nucleus of an atom, which uniquely identifies each element.
3. Recognize that atomic mass and mass number relate to the total number of protons and neutrons, but do not determine the element's position in the periodic table.
4. Note that the number of neutrons can vary among isotopes of the same element, so it is not used for the arrangement.
5. Conclude that the atomic number is the key number that determines the arrangement of elements in the modern periodic table.