What element has the symbol 'Tm'?

The story behind the answer

Tm is the symbol for Thulium, a lanthanide (rare-earth) metal with atomic number 69. The other options have distinct symbols: Tantalum = Ta, Titanium = Ti, and Thorium = Th. Notice how Thulium’s symbol uses its first and last letters—T and m.

Thulium is named after “Thule,” an ancient name for Scandinavia, and is one of the rarest naturally occurring lanthanides. It’s used in specialized lasers (e.g., Tm:YAG) and in portable X-ray sources via the isotope Tm-170. Memory tip: think “ThuM-lium” to link the M in the name to the M in its symbol, and “Thorium is Th,” leaving Tm for Thulium.