Step 1: Metals used in the Indus Valley Civilization.
The Indus Valley people primarily used Copper, Tin, and Bronze, but iron was not used by them. They had advanced knowledge of working with copper and bronze for tools, weapons, and other artifacts.
Step 2: Conclusion.
Iron was not utilized by the people of the Indus Valley Civilization, as it was not discovered until later periods in history.
Final Answer: Iron.