Answer:
2. an atom
Step-by-step explanation:
Which of these options is the smallest particle?
The answer is an atom.
It's smaller than a molecule; it's smaller than water drops and specks of dust.
Water drops and specks of dust can be seen by our eyes; however, molecules and atoms are too small for us to see, and they can only be seen under a microscope.
So, Out of the four options provided, an atom is the smallest one.