The strongest laboratory emission-line wavelengths (in nm) for three pure elements are listed below.
Element P: 410, 434, 486, 656
Element Q: 447, 468, 588, 668
Element R: 589, 590, 819
An unknown discharge tube produces bright lines at 410 nm, 486 nm, and 656 nm. Determine which element (P, Q, or R) the unknown gas most likely contains and state your evidence in one sentence.