1. Amy's science teacher shows her class a model of an atom. Why is a model useful for studying atoms? A. All atoms exist in the gas phase, and atmospheric gases are invisible.
B. A model is helpful to observe the behavior of the parts of an atom.
C. The parts of an atom cannot be directly observed.
D. A model of an atom is the same for all atoms.

The parts of an atom cannot be directly observed.

Explanation:

An atom is the smallest indivisible particle of a substance that can take part in a chemical reaction.

Atoms are not observed with naked eyes because they are found in the realm of very small particles. It is impossible to observe the parts of an atom directly.

As a result of this, models suffice in explaining the parts of an atom. Hence the answer.