After chloroflurocarbons were banned, which class of chemicals was used in their place?
a. hydrofluorocarbons
b methane
c. sulfur dioxid
d. carbon dioxide

C. Sulfur dioxide

Explanation:

Sulfur dioxide is a dangerous chemical, and it may create complications. An ingredient incorporated in the making of sulfuric acid because it is widely used in many industries. When starting a car in the morning, one interacts with Sulfur, and this is experienced when striking a match.

The substance is usually colorless and soluble in water forming a gas. Sulfur is not, however flammable, but it has a transition that happens during the volcanic and produces a waster product with materials that are heated.

81 is a composite number.