Short answers, pulled from the story.
Lead is a chemical element with the symbol Pb, from the Latin plumbum, and atomic number 82. It is a heavy, soft, malleable post-transition metal that is denser than most common materials and has the highest atomic number of any stable element.
Lead has a density of 11.34 grams per cubic centimeter, greater than iron at 7.87, copper at 8.93, and zinc at 7.14. Its close-packed face-centered cubic structure and high atomic mass account for the weight, which gave rise to the idiom to go over like a lead balloon.
Lead is a neurotoxin that accumulates in soft tissues and bones and has no confirmed safe level of exposure. It binds to sulfhydryl groups on enzymes and mimics calcium, iron, and zinc, crossing the blood-brain barrier, degrading myelin sheaths, and disrupting heme synthesis to cause microcytic anemia.
The largest use of lead in the early 21st century is in lead-acid batteries. It is also used for radiation shielding, sailboat keels, scuba diving weight belts, sound-deadening studio walls, bullets, and construction roofing, and in 1993 some 600 tonnes stabilized the base of the Leaning Tower of Pisa.
Lead comes from primary production using mined ores, mainly galena, and from secondary production using scrap. In 2022 global production was about twelve million tonnes, roughly two thirds of it from recycling, with spent lead-acid batteries the most important source for recycling.
Most primordial lead was created by repeated neutron capture in stars through the slow s-process and the rapid r-process, the latter occurring in supernovae or neutron star mergers. The amount of lead in the universe slowly increases as heavier unstable atoms decay down to it, and three lead isotopes are the endpoints of major nuclear decay chains.