Question

what is the chemical formula for concentrated plutonium exploding and igniting hydrogen and how could it be stabilized? i'm not doing this IRL, so don't worry!

Answer 1

Basically, an atomic bomb relying on pure fission like a plutonium bomb works by chain reactions. However, something must initiate the chain of reactions : that's where Hydrogen comes in:

the fission reaction of Uranium is $U+n\rightarrow Sr+Xe+2n$ where n is a neutron. Hydrogen is basically a neutron and an electron; it's thus quite easy to start the reaction with hydrogen.

There is no known way to significantly reduce radioactive decay as far as I know (I might be wrong), or to turn radioactive plutonium into non-radioactive plutonium without tearing the molecules apart.