The correct answer is: b) 3,500 BCE.
The Chalcolithic Period, also known as the Copper Age, is a period in human history when copper was first used to make tools and weapons. It is a transitional period between the Neolithic Period, when stone tools were the primary means of production, and the Bronze Age, when bronze tools and weapons became more common.
The Chalcolithic Period began in different parts of the world at different times. In the Indus Valley, it began around 3,500 BCE. During this time, people in the Indus Valley began to use copper to make tools and weapons. They also began to build large cities, such as Harappa and Mohenjo-daro.
The Chalcolithic Period ended around 2,000 BCE, when bronze tools and weapons became more common. This was also the time when the Indus Valley Civilization began to decline.
The other options are incorrect because:
- Option a) is too early. The Chalcolithic Period did not begin until around 3,500 BCE.
- Option c) is too late. The Chalcolithic Period ended around 2,000 BCE.
- Option d) is incorrect because it is not a specific date.