Chemicals & uses: Potassium nitrate (KNO3) is commonly used in which of the following? Think of its role as an oxidizer in classical compositions. Choose the correct application.

What is being asked?
The principal traditional application of potassium nitrate.

Given data

• Chemical: KNO₃ (saltpetre)

Concept/Approach
Potassium nitrate acts as an oxidizer in black powder (classic ratio ~75% KNO₃, 15% charcoal, 10% sulfur) and in many pyrotechnic compositions → hence its use in gunpowder and fireworks.

Note
It also finds use in fertilizers and meat curing, but the hallmark exam answer is its role in propellants/pyrotechnics.

Final Answer
Gunpowder and fireworks (oxidizer in propellants)