What element has the symbol 'Pa'?

The story behind the answer

The symbol Pa stands for Protactinium, an actinide element with atomic number 91. Its name comes from “proto-” (meaning parent or precursor) and actinium, because protactinium decays to actinium in natural radioactive series. It’s extremely rare and highly radioactive, occurring in trace amounts in uranium ores.

Memory tip: Precious metals have neat, name-like symbols—Palladium is Pd and Platinum is Pt—while Phosphorus is simply P. That leaves Pa for Proto-actinium, the “parent” of actinium (Ac). Think “Pa → parent of Ac” to lock in that Pa is Protactinium.