The correct answer is: c) Mesolithic.
Microliths are small, stone tools that were used during the Mesolithic period. They were made by flaking off small pieces of stone from a larger piece, and they were used for a variety of purposes, including hunting, fishing, and woodworking.
The Mesolithic period was a time of transition between the Paleolithic period, when humans were hunter-gatherers, and the Neolithic period, when humans began to practice agriculture. During the Mesolithic period, humans began to develop new technologies, such as the use of microliths, and they began to live in larger, more permanent settlements.
The discovery of microliths in Arunachal Pradesh suggests that humans were living in the region during the Mesolithic period. This is supported by the fact that microliths have also been found in other parts of India that are known to have been inhabited during the Mesolithic period.
The other options are incorrect because they do not correspond to the time period when microliths were used. The Paleolithic period was a time when humans used large, stone tools, and the Neolithic period was a time when humans began to use polished stone tools. The Bronze Age was a time when humans began to use bronze tools.