What element has the symbol 'Pu'?

The story behind the answer

Pu is the symbol for Plutonium, an actinide. The other options have symbols Pd (Palladium), Po (Polonium), and Pa (Protactinium). A handy cue: think "Pluto -> Pu."

Plutonium was first synthesized in 1940 at Berkeley and named after the planet Pluto, following the celestial theme: Uranium (Uranus) -> Neptunium (Neptune) -> Plutonium (Pluto). It’s a dense, radioactive metal; isotope Pu-239 fuels nuclear reactors and weapons, while Pu-238 powers deep-space probes via radioisotope generators. Remembering the planet sequence and the "Pu" sound makes the match stick.