The correct answer is: a) Karbi Anglong and neighboring areas.
Mica is a mineral that is used in a variety of products, including electronics, insulation, and roofing. It is found in many parts of the world, but the largest deposits are in India. In Assam, mica is found in the Karbi Anglong district and neighboring areas. The demand for mica is increasing due to its use in the electronics industry.
Option b) is incorrect because the river plains of Brahmaputra are not a major source of mica. Option c) is incorrect because the Barak valley hills are not a major source of mica. Option d) is incorrect because the Himalayan foothills are not a major source of mica.