Potassium nitrate

Is potassium nitrate explosive?

It is not combustible, however, I does accelerate the rate at which other combustible materials blow up. So it does not start fires or explosions directly, but it can act as a catalyst

It isn't a catalyst in the scientific sense, it gets used up in the chemical reaction. It's a strong oxidizing agent as it decomposes so it's roughly one half of an explosive. You need to have something to oxidize to lead to combustion or explosion.

Like sugar?

Sugar is something that gets oxidized. It has some oxygen in it but the main reaction is sugar mixes with O2.

Potassium nitrate is supplying oxygen to a reaction, it's KNO3. Those 3 oxygen atoms break off and combine with combustible material. Having a supply of reactive oxygen mixed throughout a solid material allows for combustion way faster than waiting on oxygen from the air.

There's a science experiment they do in intro chem labs where you drop a gummy bear inside of a tube full of a chemical similar to potassium nitrate that's been heated up to its decomposition point. The gummy bear burns like a signal flare for about 10 seconds as all of the energy inside of it is burned rapidly.

nope, just put it in water