Final answer:
In chemistry, the number 3 in the expression 3CO2 is a coefficient representing three molecules of carbon dioxide, while the number 2 is a subscript indicating that each molecule contains two oxygen atoms.
Step-by-step explanation:
In the expression 3CO2, the numbers 3 and 2 are, respectively, a coefficient and a subscript. Coefficients tell us how many molecules or units of a substance are involved while subscripts indicate the number of atoms of the element that are in one molecule of the compound.
For instance, in CO2, the number 2 as a subscript denotes that there are two oxygen atoms bonded to a single carbon atom in a carbon dioxide molecule. Conversely, the coefficient 3 means we have three separate molecules of carbon dioxide.
Recognizing the difference between coefficients and subscripts is fundamental in understanding chemical equations, as they determine the stoichiometry of a reaction.
When reading and writing chemical formulas and equations, it's essential to interpret these numbers correctly to accurately convey the composition and the quantities of reactants and products.