The noun trichloromonofluoromethane can be countable or uncountable.

In more general, commonly used, contexts, the plural form will also be trichloromonofluoromethane.

However, in more specific contexts, the plural form can also be trichloromonofluoromethanes e.g. in reference to various types of trichloromonofluoromethanes or a collection of trichloromonofluoromethanes.