What element has the symbol 'Tl'?

The story behind the answer

Tl is the symbol for Thallium. The other choices have different symbols: Tantalum is Ta, Titanium is Ti, and Tellurium is Te.

Thallium was discovered in 1861 by William Crookes via spectroscopy and named from the Greek “thallos,” meaning “green shoot,” after its bright green spectral line. It’s a heavy, soft, highly toxic metal in group 13, used historically in rat poison and today in specialized optics and electronics. Memory tip: think “ThaLlium” with its prominent L sound—Tl—while Ta (Tantalum), Ti (Titanium), and Te (Tellurium) each mirror their first two letters.