1: A fluorine gas concentration of only 0.1 percent will prove fatal if inhaled for even just a few minutes!
2: J. Environ. Monit., 2005, 7, 11–15.
3: Deuterons are nuclei of deuterium, the isotope of hydrogen containing one proton and one neutron in its nucleus.
4: Via the spontaneous fission of uranium ores.
5: Aqua regia, from the Latin for royal water, is a highly corrosive, fuming, yellow/red mixture of nitric acid and hydrochloric acid (1:3) capable of dissolving most metals, including gold.
6: The middle of the periodic table as it’s normally presented, that is, with the lanthanoid and actinoid rows displayed beneath the main body of the table.
7: Something similar happens with argon (39.95) ...