Here's why:

* Closely packed particles in a regular pattern is the defining characteristic of a solid.

* Bromine exists as a diatomic molecule (Br₂) at room temperature. This means two bromine atoms are bonded together.

* The weak intermolecular forces between bromine molecules are strong enough to hold them close together in a liquid state at room temperature.

However, bromine can become a solid at lower temperatures. The specific temperature at which it freezes is -7.2°C.

So, while a closely packed, regular arrangement of particles is typical of solids, bromine's behavior is determined by its intermolecular forces and temperature.