The correct answer is B. Samastipur.
Saltpetre is a mineral that is found in the earth’s crust. It is a white, crystalline substance that is used in the manufacture of gunpowder, fertilizer, and other chemicals.
Samastipur is a district in the state of Bihar, India. It is located in the north-central part of the state, and is bordered by the districts of Darbhanga, Begusarai, Vaishali, and Patna. The district has a population of over 3 million people, and its headquarters is the town of Samastipur.
Saltpetre is found in the district of Samastipur in the form of a mineral called carnallite. Carnallite is a white, crystalline mineral that is composed of potassium chloride, magnesium chloride, and water. It is found in the form of veins and nodules in the earth’s crust.
The saltpetre industry in Samastipur is a major source of employment for the people of the district. The industry is responsible for the production of millions of tons of saltpetre each year. The saltpetre is used in the manufacture of gunpowder, fertilizer, and other chemicals.
The saltpetre industry in Samastipur is facing a number of challenges, including the depletion of the saltpetre reserves, the increasing cost of production, and the competition from other countries. However, the industry is still a major source of employment and revenue for the district of Samastipur.
The other options are incorrect because they are not districts in the state of Bihar.