Liquid oxygen is blue.
Some radioactive elements really do glow.
You can die from drinking too much water.
If you mix half a liter of alcohol with half a liter of water, the volume of the mixture will be less than one liter.
Liquid water is more dense than solid water (ice).
You can melt a sample of the element gallium just by holding it in your hand.
Under certain conditions, hot water will freeze more quickly than cold water.
You can't solidify helium at normal pressures, even at absolute zero. (You can solidify it at extremely high pressure and low temperature.)