Context: This passage describes a chemical reaction. Read the passage. Then, follow the instructions below.
People have used gunpowder as an explosive for hundreds of years. Gunpowder is a mixture of three different substances: potassium nitrate, charcoal, and sulfur. When these substances are burned together, they release a large amount of heat and gas. In the past, gunpowder was used in muskets and cannons, but today, it is mainly used in fireworks.
Complete the sentence.
In this chemical reaction, potassium nitrate is a ().
A. product
B. reactant
From the given choices, select the correct answer and reply with the letter of the chosen option.

B