Now, molecularity is associated with a number of moles for reactant molecules within an elementary step. Here we take a look. We have one mole of carbon dioxide gas reacting with one mole of water liquid to produce one mole of carbonic acid. If we were to take a look here, we'd say that we have a total of 2 moles of reactants.
Now the number of moles of reactants gives us different names for the molecularity. If we had only one mole of a reactant then the molecularity would be called unimolecular. If there are two moles of reactants like we have in this example, then that would be called bimolecular. Now I know when we're naming covalent compounds in the past when we say 2:00 we'd say die like carbon dioxide. But for molecularity we don't use the prefix dye, we use the prefix by SO2 moles of reactants equals bimolecular.
If we add 3 moles of reactants total, then that would be termolecular. When we talked about numerical prefixes in the past, three would be try. But there's no such thing as trimolecular. So again when it's 3 moles of reactants it's termolecular. So when we talk about molecularity, just count the total number of reactant molecules and you'll be able to determine the molecularity of any elementary step.