Hydrogen was an element on the periodic table with the symbol H (PROSE: Christmas on a Rational Planet [+]Loading...["Christmas on a Rational Planet (novel)"]) and atomic number 1. (TV: Shada [+]Loading...["Shada (TV story)"]) It was the most abundant element in the universe. A hydrogen in-rush was a crucial part of Event One. (TV: Castrovalva [+]Loading...["Castrovalva (TV story)"])
The Earth's Sun was made up of 74% hydrogen and 24% helium. (AUDIO: Feast of Fear [+]Loading...["Feast of Fear (audio story)"])
Hydrogen and oxygen made up H₂O (PROSE: Christmas on a Rational Planet [+]Loading...["Christmas on a Rational Planet (novel)"]) or water. (TV: Arc of Infinity [+]Loading...["Arc of Infinity (TV story)"])
The Fourth Doctor suggested energising hydrogen as an alternative power source to the "mineral slime" oil. (TV: Terror of the Zygons [+]Loading...["Terror of the Zygons (TV story)"])
Hydrogen could be used as a base in the process to form huon particles. (TV: The Runaway Bride [+]Loading...["The Runaway Bride (TV story)"])
The R101 was filled with hydrogen gas. (AUDIO: Storm Warning [+]Loading...["Storm Warning (audio story)"])
The Skelloids' life cycle relied on the absorption of hydrogen through their gill-plates. Banto Zame, posing as the Doctor, seemingly foiled an invasion of the Generios system by the Skelloids by exploiting this by using his psychic screwdriver to invert the core of their hydrogen stabilisers. In reality, the Skelloid invasion was nothing but a mere holographic illusion created by him. (AUDIO: The One Doctor [+]Loading...["The One Doctor (audio story)"])
Among other chemicals, the Source contained hydrogen, which helped allow it to act as a terraforming agent. (TV: The Doctor's Daughter [+]Loading...["The Doctor's Daughter (TV story)"])