Three conical flasks, each containing a different halogen. They are chlorine (Cl, pale green), bromine (Br, red brown) and iodine (I, pale purple). The halogens are in Group 17 of the periodic table. They form diatomic molecules in their elemental form, react with water to form acids and are toxic and corrosive. Group 17 is the only group to contain representatives of all three states of matter at room temperature - gas (chlorine), liquid (bromine) and solid (iodine).