Which concept addresses the nature of matter, defines the fundamental elements, and explains how atoms form compounds and take part in chemical reactions?

• A. Quantum theory
• B. Kinetic theory
• C. Molecular theory
• D. Atomic theory

Answer: (D)

Atoms are the basic building blocks of matter. Atomic theory states that matter is made of atoms, and each element is defined by its own type of atom. When atoms bond, they combine in definite ratios to form compounds, and chemical reactions are rearrangements of those bonds that conserve the atoms involved. The modern view adds subatomic particles and electron behavior, but the core idea remains that the identity of substances comes from the kinds of atoms and how they bond. Other theories describe related aspects, but atomic theory best explains the nature of matter, the definition of elements, and how atoms form compounds and participate in reactions.