Which is called Indian Saltpeter?

Hint: Potassium nitrate is called the Indian saltpeter because it is one of the most important nitrogen containing compounds that is used as a crude salt in India. It is also known as niter. It is an ionic salt of potassium ion and nitrate ion.

Complete answer:
The chemical formula of Indian Saltpeter or Potassium Nitrate is $KN{O_3}$. It is a black coloured solid. The production of Potassium nitrate is a very ancient work in India, it is extracted from soil from the villages where it is formed by bacterial decomposition of organic matter. It has many applications some of them are
-Potassium nitrate was used as an oxidizer in black powder which was used in ancient times as an explosive all around the world. It is also a major constituent of gunpowder.
-Potassium nitrate is a common ingredient in meat processing. It is also used in food preparation for thickening agents in soups.
-Potassium nitrate is used in fertilizers as it contains nitrogen and oxygen, two main macronutrients for plants.
-It has many medical uses like It used in Toothpastes for sensitive teeth, it is used in curing asthma, used as main ingredient in kidney tablets for treatment of cystitis, it is used to treat high blood pressure.
-It is used as electrolyte in salt bridges.
-It is used as an aluminium cleaner.
-It is a component of tree stump removal products.

Note:
Structure of Potassium Nitrate is an orthorhombic crystal at room temperature, it is moderately soluble in water but its solubility increases with temperature. It can react explosively with alcohol but is not explosive on its own.