These are all chemical formulas representing different compounds:

H2: This represents dihydrogen, which is a molecule consisting of two hydrogen atoms bonded together.HBr: This represents hydrogen bromide, which is a colorless gas with a sharp, pungent odor.CaBr2: This represents calcium bromide, which is a white crystalline solid used as a drilling fluid in the oil industry.AgBr: This represents silver bromide, which is a light-sensitive chemical used in photography.