Oh my, how do you pick one?
For the dissolving metal reductions.
When I was in grad school, I ran lithium - refluxing liquid ammonia dechlorination reactions, usually on a 2.5L scale, because for one compound, that was step three out of sixteen- and after step sixteen came photochemical studies (and sodium ethanol reduction did not work for any of my compounds).
I had my very own personal ammonia gas cylinder..
For this reaction, after one condenses the ammonia in a -78C (dry ice acetone) bath it is important to let the ammonia warm up almost to reflux (-33C) before slowly adding the lithium. If you do not, the lithium dissolves and re-precipitates as tiny particles of the metal. These react a little too rapidly as the reaction mixture eventually warms up- and well, you won't enjoy that brilliant blue, because you will be too busy trying to avoid a "major chemical incident", and then of course there's the cleanup of the back wall of the hood, and the re-synthesis of the starting materials...
Fortunately I learned the lesson on 500 ml scale, and enjoyed calmly watching that most beautiful color of blue many many times.
Ahhhh, those were the days.
Maybe it is Thorium? Because there is so much ado about molten salt reactors fed with Thorium. And this reactors might be able to transmute the nowadays nuclear wast to usefull and/or fast decaying products.