Which of the following is a brown to black-colored American beer style with normal to elevated alcohol content (4.8-6.5% ABV) and pronounced bitterness?

The correct choice is American Porter, which is characterized by its brown to black color, normal to elevated alcohol content ranging from 4.8% to 6.5% ABV, and a distinct bitterness. Porters are known for their roasted malt flavors, which contribute to the darker hue and a range of flavor notes, often including chocolate and coffee. The bitterness in American Porter comes from the use of hops, which balances the malt sweetness and adds complexity to the beer.

American Lager, while a popular style, typically has a lighter color and a more subdued hop presence, resulting in a lower bitterness. American Brown Ale is also brown in color but generally has a maltier sweetness and is less pronounced in bitterness compared to a porter. American Stout shares similarities with Porter but usually leans toward a darker, more intense profile with a higher alcohol percentage and deeper roasted flavors. Thus, the identification of American Porter aligns perfectly with the description provided in the question.