@Davidzilla chlorine could be CAUS (which is already a toxic, reactive, green gas), and your sodium seems like RBDM. Just make RBDM and CAUS combine to make SALT.
also it can be contained with crmc - its melt point will be inf becuz of inf psi but temperature is inf so ceramic will turn into semi real object that cant be real so u will create 2 singularities
btw, to make something resistant to DEST, set its weight property to 102.
how about graphite (GRPH)? It would slow down and absorb neutrons, convert nearby molten IRON to molten METL, deco nearby PLNT black, sublimates at extremely high temperatures (around 4000 Kelvin), glows red, yellow, and then white as you increase the temperature, be resistant to DEST, and be produced by exposing COAL or BCOL to temps above 1000C and pressures below -20.
inf pressure + uranium will create a singularity like in blackhole laws of physics wont work in inf pressure and inf heat its blackhole
I actually tried to add a moving solid in a Lua mod once - it just started spinning like crazy and producing infinite pressure
what about elements that dont exist irl?
no one uses californium for start up reactor
Add a liquid element with high surface tension, so it forms into ball you can fly with by dumping powders on