John Dalton proposed that elements are made of tiny, solid balls called ______.

• A. Protons
• B. Electrons
• C. Neutrons
• D. Atoms

Answer: (D)

Dalton’s atomic theory describes matter as built from tiny, indivisible units called atoms. He pictured elements as composed of their own kind of atom, each atom being a solid sphere that cannot be broken down by chemical means. That’s why the term fits: atoms are the basic building blocks Dalton proposed. Protons, electrons, and neutrons are subatomic particles that make up atoms, discovered after Dalton’s time, so they describe parts inside an atom rather than the fundamental unit Dalton introduced.