In Chemistry, we often use formulas to represent what is present in a sample of matter. The formulas consists of letters - known as elemental symbols - and two types of numbers - known as coefficients and subscripts. The elemental symbols indicate what types of atom are present. Each element has its own unique symbol ... such as H for Hydrogen and O for oxygen. When we see two or more of the same type of atom bound together in a single unit, we use a subscript to indicated the number of that type of atom. For instance, the number 2 in H₂O indicates that there are two H atoms in a particle of water. When there are two or more of a particular unit, we use a coefficient in front of the formula in order to indicate the number of units of that formula. For instance, the number 3 in 3 H₂O indicates that there are three water molecules present in the sample.
 

Particles .. Words .. Formulas. They are all ways to represent what is present in a sample of matter. This question tests your ability to recognize the way to represent matter using formulas. Study the diagram below to inform yourself about the topic. Then answer the question.