Select the elementary substance.

 - bromomethane (CH3Br)
 - water (H2O)
 - diamond (C)
Look at the chemical formula for each substance, and count the number of symbols in the formula. Then, decide if the substance is an elementary substance. The chemical formula for diamond contains one symbol: C for carbon. So, diamond is made of one chemical element. Substances that are made of one chemical element are elementary substances. So, diamond is an elementary substance. The chemical formula for bromomethane contains three symbols: C for carbon, H for hydrogen, and Br for bromine. So, bromomethane is made of three chemical elements bonded together. Substances that are made of two or more chemical elements bonded together are compounds. So, bromomethane is a compound, not an elementary substance. The chemical formula for water contains two symbols: H for hydrogen and O for oxygen. So, water is made of two chemical elements bonded together. Substances that are made of two or more chemical elements bonded together are compounds. So, water is a compound, not an elementary substance.