________________ is the scale used to relate specific gravity of a beverage such as Diet Coke® to sugar content.

The correct answer is Brix. This scale specifically measures the sugar content in a solution, such as beverages like Diet Coke. Brix is defined as degrees Brix (°Bx), where one degree corresponds to 1 gram of sucrose in 100 grams of solution. This measurement is particularly relevant in food science for determining the sweetness and quality of various liquid products, enabling manufacturers to tailor their beverages according to consumer preferences.

The relationship between specific gravity and sugar content is well established; as the sugar content increases, the specific gravity of the solution also tends to increase. This makes Brix an essential tool in the beverage industry for quality control and product formulation. Understanding Brix allows producers to produce consistent products with desired taste profiles.

Other options, such as water activity, viscosity, and total solids, do not directly measure sugar concentration in the same manner. Water activity accounts for the amount of water available for microbial growth; viscosity measures a fluid's resistance to flow; and total solids includes all solids present in a solution, not just sugars. These metrics may be important in specific contexts but do not relate specifically to the sugar content in beverages like Brix does.