Final answer:
Lead is used by fire investigators as a temperature marker because of its low melting point, which provides insights into the intensity of a fire when examining a scene.
Step-by-step explanation:
Among the listed metals, lead is used by fire investigators as a temperature marker due to its low melting point. Lead melts at around 327.5 degrees Celsius (621 degrees Fahrenheit), which is significantly lower than the melting points of the other metals mentioned, such as aluminum, copper, and iron. Therefore, melted lead can indicate that a fire reached at least the melting point of lead, providing useful information about the fire's temperature. This practice allows fire investigators to assess the intensity of the heat in different areas of a fire scene.