there are more than one
1- the interesting one if you add manage oxide as catalyst to concentrated hydrogen peroxide it will make a highly strong effervescence to produce oxygen gas, but keep it safe as this is dangerous experiment.
2- if you mix concentrated hydrogen peroxide with liquid soap and then add potassium iodide it will make instantaneously a column of foam and this is funny experiment, I recommend you to do it.
I like working with isotopes – atoms o the same element with different masses. You can get really clear answers to chemistry questions by doing some experiments with isotopes and following the reaction using a mass spectrometer.
There are a few experiments I really like doing, this one is really nice and “dangerous” (but I’m extra extra careful!) which involves condensing ammonia (which is a gas) in a round bottom flask using liquid nitrogen. Then I shave into it sodium metal (which has the consistency of hard cheese) and the ammonia which is colourless turns deep blue! I put in my substrate to remove part of it under this conditions and the reaction is complete in 5 minutes! The work up involves evaporating the ammonia in the fumehood and filtering off the product. Done!