Liquid Nitrogen

Most chemicals have the 3 classical phases, but with the possible exception of water, none are as fun as liquid nitrogen (LN). Sure, other gasses are chilled to liquids, but none are as common, cheap (like the price of milk), or easy to work with.

At a chilly 77K (−196 °C; −321 °F) it is the quickest way to play with cryogenics or just freeze things instantly.

Who does not love to see a drop of liquid nitrogen hover above the ground, vibrating as if it is about to rip itself apart. And notice, it doesn't touch the ground so much, as hover above it. The gas that comes from boiling from being in contact with something warm, that gas expands so much that it lifts the drop up just a bit.

Of course, that is not say it isn't good at freezing whatever it does come in contact with. It is fantastically good at that because it is so much colder than anything else we commonly come in contact with - cold enough to freeze something brittle enough to shatter, like a banana or a rose.

Of course, liquid nitrogen does have its uses beyond goofing off!

It is the best way to freeze something really solid or to preserve it indefinitely. If you need to work with something very cold or exceptionally dry.... this is the way to go. And it is standard issue for dealing with high temperature superconductors, at least until we have room-temperature ones. It is even good for freezing your head, Futurama-style until we can cure whatever ails you!