Yominum sulfide

From Memory Alpha, the free Star Trek reference.

Yominum sulfide is a chemical with a molecular formula of K₄YM₃(SO₇³ES₂).

When Spock was performing a memory test, one of the questions asked him what the molecular formula for yominum sulfide was. (Star Trek IV: The Voyage Home)

Yominium was named after Leonard Nimoy – "Yomin" is "Nimoy" spelled backwards.