Which concept naming the nature of matter and how atoms form compounds is described by which theory?

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

Answer: (A)

The main idea being tested is the description of matter at the atomic level and how atoms come together to form substances. Atomic theory states that matter is made of tiny particles called atoms, that atoms combine in simple whole-number ratios to form compounds, and that chemical reactions involve rearrangement of atoms while preserving their total amount. This directly explains both what matter is and how atoms form compounds, making it the best match.

Kinetic theory focuses on how particles move and how this affects states of matter, not on the fundamental nature of matter or the formation of compounds. Quantum theory deals with behavior of matter and energy at atomic scales, such as energy levels and probabilities, rather than the broad description of matter’s nature or compound formation. Molecular theory centers on molecules and their properties, which is related but does not name the foundational idea that all matter is composed of atoms and that they combine to form compounds in fixed ratios.