1. This element was discovered in 1807 in London. It is essential to all living things. In water, it reacts rapidly to release hydrogen, and burns with a lilac-coloured flame. Calcium Magnesium Iron Potassium

2. This element is considered dangerous in all its forms. It takes its name from the planet whose name is equivalent to the Greek god, Hermes. Mercury Krypton Plutonium Neptunium

3. This element was discovered in 1811 in Paris, France. It comes as black, shiny crystals that dissolve in alcohol, the result of which is sold as an antiseptic solution. Hydrogen Peroxide Iodine Magnesium Gallium

4. This radioactive element was discovered in 1964 in Dubna, Russia, and is not a naturally-occurring element. Only a few atoms have ever been made, and it is of research interest only. Californium Uranium Dysprosium Rutherfordium

5. The well-known name for this element comes from the Anglo-Saxon word "seolfur," although its chemical symbol is derived from its Latin name. Sulphur Silver Stannum Silicon