The 39 Clues Wiki
The 39 Clues Wiki

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Hydrogen is an Ekaterina Clue and is part of Gideon Cahill's master serum.



The Hydrogen Symbol

The research facility CERN is open to scientists all over the globe. However, it is also a secret Ekaterina stronghold. The Clue was hidden in the stronghold.

Card Combo[]

This Clue can be unlocked by completing the Cahill Collision Card Combo:



Hydrogen is a gas at room temperature. It's the lightest element, and is commonly used in balloons and other floating objects because of this. It is a somewhat abundant chemical.

It is the most abundant element in the universe.

It is also placed in the periodic table as "1" in the elements.

It`s symbol is "H"

Hydrogen Glow

Hydrogen Glow


In the cutscene, an Ekaterina research paper for CERN is shown. The screen zooms in on the paper several times in several places. The circle in the center glows and becomes a hole. The screen goes down the hole, revealing the letter H, which becomes the word "HYDROGEN" (faintly glowing blue) with a flash of many different colors and a loud static noise.


The 39 Clues - Clue ? 2 - Hydrogen


  • Along with Rosemary, they are the easiest clues to be collected, unlike other one-card requiring card combos, Hydrogen and Rosemary are the only common/uncommon card which means it only needs one card replicator.