Potassium

Potassium was an element.

The Ninth Doctor claimed bananas were a good source of potassium. (TV: The Doctor Dances)

Potassium nitrate and sulphur were constituents of gunpowder. (TV: The Visitation)

Thea Ransome performed a potassium-argon test in the dating of "Eustace". (TV: Image of the Fendahl)

Potassium Street a street in Paradise Towers. (TV: Paradise Towers)