Name the element
In 1967, the Thirteenth General Conference on Weights and Measures gave the current scientific definition of the second to be the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the BLANK-133 atom.
Identify this element discovered by Bunsen and Kirchoff, the first to be discovered spectroscopically, which was given a name derived from the Latin for "blue-grey" or "sky blue", so named for the strong blue line in this element's emission spectrum.
Cesium (Cs)