Solid carbon dioxide (CO2) is known as dry ice. It sublimes at --78 °C, becoming an extremely cold gas. It is often used in theatres or nightclubs to produce clouds (looking a bit like smoke). It is more dense than the air, so it stays low. It cools the air and causes water vapour in the air to condense into tiny droplets, hence the "clouds".

It is also useful in the physics (and chemistry) laboratory.

For more information and the full suite of resources, visit iop.org/radioactivity

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