Potassium

Potassium was an element. K9 Mark II concured that it was highly conductive to health. (COMIC: Death to the Doctor!) It was a vital nutrient and was necessary for living things to grow. (TV: The Waters of Mars)

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)