Final answer:
Silver has the lowest resistivity at 20°C compared to aluminum, brass, and copper, due to its high density of free electrons which makes it an excellent electrical conductor.
Step-by-step explanation:
The student has asked which material among aluminum, brass, copper, or silver has the lowest resistivity at 20°C. Based on electrical conductivity, which is inversely related to resistivity, and given that both are strongly correlated to the density of free electrons in a material, silver has the lowest resistivity of the materials listed at room temperature. This is confirmed by data that recognizes silver as one of the best electrical conductors, along with copper, gold, and aluminum.
It's also important to understand that while copper has a lower resistivity than aluminum according to comparison statements, implying a need for a smaller diameter of copper for the same length of aluminum to conduct the same amount of electricity, silver tops the list in electrical conductivity. So even when compared to copper, silver exhibits the lowest resistivity. These properties of materials are essential, especially when considering applications such as the design of cooking utensils, where good conductors are used for efficient heat distribution.