Atomic number describes the number of protons and defines the element. Which option states this?

• A. The Number of Protons and Defines the Element
• B. The Number of Protons and Neutrons
• C. The Total Electrons
• D. The Total Mass

Answer: (A)

Atomic number is the count of protons in the nucleus, and it uniquely identifies the element. The description that the atomic number is the number of protons and that this defines the element is the best choice because protons determine which element an atom is; isotopes share the same proton count but differ in neutrons, so their mass changes while their identity does not. The other options mix in neutrons, electrons, or total mass, which are not what defines the element: neutrons vary among isotopes, electrons change with charge, and total mass is protons plus neutrons. So the statement about the number of protons defining the element matches exactly what the atomic number represents.