The correct answer is: a) Copper along with stone tools.
The Chalcolithic period, also known as the Copper Age, was a period of human development that began around 5,000 BC and ended around 3,000 BC. During this time, humans began to use copper tools and weapons, along with stone tools. Copper is a relatively soft metal, so it was often used in combination with stone to create tools that were both strong and durable. The Chalcolithic period was a time of great innovation and progress, and it laid the foundation for the development of the Bronze Age.
Option b) is incorrect because iron was not used until the Iron Age, which began around 1,200 BC. Option c) is incorrect because bronze is an alloy of copper and tin, and it was not developed until the Bronze Age. Option d) is incorrect because gold is a precious metal that was not used for tools or weapons during the Chalcolithic period.