Depends what you want to blow up – explosions occur when you have a system with has “too much energy” or can go to a more stable system by releasing energy – so you can have a nuclear explosion when you create an unstable nucleus that splits or a chemical explosion when two things react and create a system of less energy releasing the excess as explosive energy – you can maximise chemical energy release by using a highly reactive element like oxygen and enhancing the rate of the reaction by using an enclosed space – better not say any more otherwise I’ll get arrested…
As a chemist, I’ve blown a fair few things up in my time. Some things I meant to and a couple took me a bit by surprise. 🙂
You need something that has tons of stored energy which, when released, produces a massive boom and the contents expands rapidly. Atomic bombs can produce a lot of damage – is it detonated when a neutron strikes the nucleus of a plutonium or uranium isotope and the nucleus splits. This then releases more neutrons, which in turn hit more atoms which causes those atoms to split. That causes a chain reation which becomes the explosion.
There are gases which, when you mix them, produce an explosion. Oxygen and acetylene, for example. Stand near that explosion and you’ll be blown off your feel and lose your hearing for some time.