Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest halogen and is a fuming red-brown liquid at room temperature that evaporates readily to form a similarly colored vapor. Its properties are intermediate between those of chlorine and iodine. Elemental bromine is very reactive and thus does not occur free in nature but in colorless soluble crystalline mineral halide salts, analogous to table salt. While it is rather rare in the Earth's crust, the high solubility of the bromide ion (Br−) has caused its accumulation in the oceans.
The noble gases (historically also the inert gases; sometimes referred to as aerogens) make up a class of chemical elements with similar properties; under standard conditions, they are all odorless, colorless, monatomic gases with very low chemical reactivity.
The six naturally occurring noble gases are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and the radioactive radon (Rn).