De or het hydrogenium?

The correct Dutch article is:

het hydrogenium

Rule Words ending in -um and -ium: usually het. See the rule
Meaning (Dutch) (verouderd, scheikunde) waterstof

How to use hydrogenium

the hydrogeniumhet hydrogenium
this hydrogeniumdit hydrogenium
that hydrogeniumdat hydrogenium
our hydrogeniumons hydrogenium
your hydrogeniumjouw hydrogenium
every hydrogeniumelk hydrogenium
which hydrogenium?welk hydrogenium?
a big hydrogenium / the big hydrogeniumeen groot hydrogenium, het grote hydrogenium

Meaning, plural, diminutive, pronunciation and translations: WikiWoordenboek (Dutch Wiktionary) (CC BY-SA 4.0). Example sentences: Tatoeba (CC BY 2.0 FR).