The correct answer is: b) Kutch district.
Bentonite is a type of clay that is formed from the weathering of volcanic ash. It is a very absorbent material and is used in a variety of applications, including drilling mud, cat litter, and cosmetics.
The Kutch district in Gujarat is one of the major sources of bentonite in India. The bentonite deposits in Kutch are found in the Rann of Kutch, a large salt marsh that covers much of the district. The bentonite is mined from open-pit mines and is then processed to remove impurities.
The bentonite from Kutch is high quality and is in demand by industries around the world. The district is home to several bentonite mines and processing plants. The industry employs thousands of people and contributes significantly to the economy of Kutch.
The other options are incorrect because they are not major sources of bentonite in Gujarat. Bhavnagar district is home to some bentonite deposits, but they are not as large or as high quality as the deposits in Kutch. Surat district and Vadodara district do not have any significant bentonite deposits.