What element has the symbol 'Bk'?

The story behind the answer

Bk stands for berkelium, atomic number 97, a synthetic actinide named after Berkeley, California, where it was discovered in 1949 by Thompson, Street, Ghiorso, and Seaborg. The other options have different symbols: Bismuth (Bi), Bromine (Br), and Beryllium (Be).

Berkelium is a transuranium, radioactive element made in particle accelerators; notably, berkelium-249 targets helped