Final answer:
Fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid at room temperature.
Step-by-step explanation:
At room temperature, fluorine and chlorine are gases because they exist as diatomic molecules, with two atoms bonded together. Bromine is a liquid because it exists as diatomic molecules but has weaker intermolecular forces compared to fluorine and chlorine. Iodine is a solid because it exists as polyatomic molecules with more atoms per molecule and therefore has stronger intermolecular forces.