B: Discovering the internal structure of the atom.
Explanation:
Dalton’s experiments with gases marked the beginning of the modern era of chemistry. The hypotheses about the nature of matter on which Dalton’s atomic theory is based can be
summarized as follows:
Elements are composed of extremely small particles called atoms.
All atoms of a given element are identical, having the same size, mass, and chemical properties. The atoms of one element are different from the atoms of all other elements.
Compounds are composed of atoms of more than one element. In any compound, the ratio of the numbers of atoms of any two of the elements present is either an integer or a simple fraction.
A chemical reaction involves only the separation, combination, or rearrangement of atoms; it does not result in their creation or destruction.
Dalton made no attempt to describe the structure or composition of atom —he had no idea what an atom is really like. But he did realize that the different properties shown by elements such as hydrogen and oxygen can be explained by assuming that hydrogen atoms are not the same as oxygen atoms.
