Silver

Silver was a metallic element on the periodic table with the symbol Ag (TV: Shada) and atomic number 47. (PROSE: Iris Wildthyme y Señor Cientocinco contra Los Monstruos del Fiesta) It had an atomic mass of 107.870 (PROSE: Wolfsbane) or atomic weight of 108 as well as high conductivity. (PROSE: Castrovalva)

In human mythology, silver could be used to kill a werewolf, particularly in the form of bullets. The First Doctor used silver bullets to kill Roberta Sampson, a werewolf. (PROSE: The Juror's Story) Silver bullets were also utilised by the Brigadier to defeat the Destroyer. (TV: Battlefield)

Similarly, Rosa Caiman had a silver knife to defend herself against werewolves. (AUDIO: Loups-Garoux)

The Fifteenth Doctor wore rings and a necklace; all made of silver. (PROSE: "Heroes of Time" [+])

The planet Megerra was rich in valuable minerals such as silver. (PROSE: Shakedown)

When forced to create EDTA to cure arsenic poisoning, Gwen Cooper used a number of ingredients in the antidote, one being silver. (TV: Rendition)