In the nineteenth century, what was known about atoms? a. the half-life of all atoms b. the exact structure of all atoms c. the number of atoms that exist in the world is increasing. d. the atom determines the chemical property of an element

the answer is D.

Explanation:

during the 19th century, the kinetic theory of gases was developed. Kinetic theory is based on the existence of atoms and molecules in random thermal motion and provides a microscopic explanation of the gas laws, heat transfer, and thermodynamics. Kinetic theory works so well that it is another strong indication of the existence of atoms. But it is still indirect evidence—individual atoms and molecules had not been observed. There were heated debates about the validity of kinetic theory until direct evidence of atoms was obtained.

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