The classification of black coffee can be a bit nuanced. The best answer among the options provided is: a) a heterogeneous mixture.
Here’s the explanation: Black coffee is made by brewing ground coffee beans, which means that it contains various compounds extracted from the coffee grounds, such as oils, acids, and flavor compounds, along with water. While these components can seem uniform when you look at a cup of brewed coffee, in reality, the coffee consists of different substances that retain their distinct characteristics. Thus, it does not have a uniform composition throughout, which is the hallmark of a heterogeneous mixture.
While one might consider it a suspension, as coffee grounds can settle at the bottom if left to sit, it is primarily regarded as a heterogeneous mixture because of the presence of varying components and their interactions. A solution, on the other hand, would imply that the components are fully dissolved and homogeneous, which is not the case for brewed coffee. As for an element, black coffee is certainly not that as it is a compound of many different substances.