Gunpowder, also referred to as 'black powder', was the only unique/known chemical explosive until the mid-nineteenth century. It contains potassium nitrate, or 'saltpeter', which is an oxidizer, and a combination of charcoal and sulphur serves as fuel. There is a known/academic consensus that gunpowder was initially invented in China as early as the ninth century. This led to its use in fireworks and in gunpowder weapons.
I am confused between the two choices for the answers though I choose unique for the first and known for the second but I am not finding the context that will complement the same.
Can anyone guide me on what should be the correct answer and why?