The correct answer is: c) Gunpowder production.
Saltpeter (potassium nitrate) is a mineral that is found in some parts of Punjab. It was historically used for gunpowder production. Gunpowder is a mixture of saltpeter, sulfur, and charcoal that is used as a propellant in firearms and explosives. It was first invented in China in the 9th century and was introduced to Europe in the 13th century. Saltpeter is also used in fertilizers, explosives, and fireworks.
Option a) is incorrect because saltpeter is not a fertilizer. Fertilizers are substances that are added to soil to improve its ability to grow plants. Saltpeter is not a fertilizer because it does not contain the nutrients that plants need to grow.
Option b) is incorrect because saltpeter is not a medicine. Medicines are substances that are used to treat or prevent diseases. Saltpeter is not a medicine because it does not have any medicinal properties.
Option d) is incorrect because saltpeter is not used for food preservation. Food preservation is the process of preventing food from spoiling. Saltpeter is not used for food preservation because it does not have any properties that prevent food from spoiling.