Hey dude. You are correct that the phase of matter (solid, liquid, or gas) is largely determined by how the atoms or molecules interact with one another as a group. The interactions are driven by factors such as temperature, pressure, and intermolecular forces.

When considering a single atom of uranium suspended in water, the concept of phases is not applicable in the same way as it would be for a macroscopic sample of uranium. This is because phases are macroscopic properties that emerge from the collective behavior of a large number of atoms or molecules. A single atom does not exhibit a phase by itself, as the phase is a result of interactions between atoms or molecules.

To answer your second question, the difference between a single uranium atom suspended in water and a single uranium atom in space would be their surrounding environment and how they interact with it. In water, the uranium atom would interact with the water molecules and any other impurities present. In space, it might interact with cosmic rays, other atoms, or molecules depending on its location. However, neither of these situations would qualify the uranium atom to be classified as a solid, liquid, or gas, as these phases emerge from the collective behavior of many atoms or molecules.

Plasma, as you mentioned, is another state of matter in which atoms are ionized, meaning their electrons are stripped away, and this occurs at high temperatures or under intense electromagnetic fields. This state is distinct from solids, liquids, or gases, which involve neutral atoms or molecules.

So, phases (solid, liquid, or gas) are macroscopic properties that arise from the collective behavior and interactions of a large number of atoms or molecules. A single atom does not exhibit a phase on its own.