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When you place a compound in a flame, the flame will change colour depending on the metal ion present in the compound.

You can use the colour of the flame to work out what metal you have in your sample. This can be very handy if you're a crime scene investigator, or a high school chemistry student trying to pass an exam.

Fair warning: Three of these are very subtly different shades of red. I'm sorry. I don't make the rules of chemistry.