This chart shows descriptions of the atoms for four different substances which substance is a solid

The answer is Object 3.

Atoms in a solid are locked and can only vibrate in one place. So, it can’t slide past each other or spread out to fill the containers (objects 1 & 4 are out). Viscous means having a thick and sticky consistency between solid and liquid, so I’m guessing it’s something like glue or syrup, which is not a solid. That leaves Object 3 left.