The model showing a molecule of a substance that is made up of three elements is model (D) because it is made up of three distinct spheres representing atoms of each element.
A molecular model is a physical model of an atomistic system that represents arrangement of atoms in molecules and their processes.
According to this question ;
Each model of molecules in the options contains spheres of different colors and sizes representing different types of atoms.
The atoms of the same element are the spheres of same color and size while atoms of different element are of different color or size.
Therefore,
The model showing a molecule of a substance that is made up of three elements is model (D) because it is made up of three distinct spheres representing atoms of each element.
(For more detail : Please look for the figure attached)
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