Which of the following was added to Dalton's atomic theory as it was refined?

• A. Atoms contain subatomic particles such as electrons, protons, and neutrons.
• B. Atoms of different elements can combine in any ratio to form compounds.
• C. All atoms of a given element have identical mass and properties.
• D. Atoms are indivisible and cannot be broken down further.

Answer: (A)

Verified step by step guidance

1. Review Dalton's original atomic theory, which stated that atoms are indivisible and cannot be broken down further.
2. Understand that later discoveries in atomic structure showed that atoms are composed of smaller particles called subatomic particles: electrons, protons, and neutrons.
3. Recognize that this discovery led to the refinement of Dalton's theory by adding the concept that atoms are divisible into these subatomic particles.
4. Note that other statements such as atoms combining in any ratio or all atoms of an element having identical mass were either modified or disproven by later research.
5. Conclude that the key refinement added to Dalton's atomic theory is the existence of subatomic particles within atoms.