Answer:
The atoms are vibrating in place.
Step-by-step explanation:
One of the properties of an ionic substance is the possession of a crystalline structure. As Gerry observed the salt under a microscope, he discovered that it has a crystalline structure. Crystalline salts are all ionic in nature, hence the salt observed by Gerry is an ionic salt.
Solids containing a definite crystalline structure always has their particles vibrating in place. This is immediately evident as Gerry looks at the salt through a microscope.