The molecules briefly form chemical bonds with nearby objects. The molecules are always in random motion. The molecules transfer an electric charge to the dust particles. The molecules frequently change shape.
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: When observing a very small piece of dust in a liquid under a microscope, the dust appears to jiggle slightly. This movement results from the dust interacting with the molecules in the liquid. What property of the molecules in the liquid causes this effect?
Possibilities:
- The molecules briefly form chemical bonds with nearby objects.
- The molecules are always in random motion.
- The molecules transfer an electric charge to the dust particles.
- The molecules frequently change shape.

The molecules are always in random motion.