Short answers, pulled from the story.
Indium is a chemical element with the symbol In and atomic number 49. It is a silvery-white post-transition metal and one of the softest elements, with a Mohs hardness of 1.2, soft enough to be cut with a knife or bitten into. It melts at 156.60 degrees Celsius and becomes a superconductor below 3.41 kelvin.
Indium was discovered in 1863 by German chemists Ferdinand Reich and Hieronymus Theodor Richter while testing ores from mines around Freiberg, Saxony. They identified it by a bright blue line in its spectrum. Richter went on to isolate the metal in 1864.
Indium is named for the indigo blue line seen in its spectrum. The name comes from the Latin word indicum, meaning violet or indigo, which also means Indian, because the dye indigo was originally exported to Europe from India.
Indium is used primarily in flat-panel displays as indium tin oxide, a transparent conductive coating on glass, and LCD production is its largest consumer. It is also used in semiconductors, low-melting-point solders and alloys, blue and white LED circuits, nuclear reactor control rods, and as the radiotracer indium-111 in nuclear medicine.
Indium is produced exclusively as a by-product during the processing of the ores of other metals, chiefly from sphalerite and other sulfidic zinc ores. During zinc smelting it accumulates in iron-rich residues and is purified by electrolysis. China was the leading producer with 290 tonnes in 2016.
Indium-115 makes up 95.7 percent of all indium even though it is radioactive, with a half-life of 4.41 years. This abundance comes from how indium forms in stars through the slow neutron-capture s-process, which produces indium-115 as the end of a decay chain starting from silver. Indium is one of only three elements, with tellurium and rhenium, whose stable isotope is rarer than its long-lived radioisotope.
Indium has no biological role in any organism studied, and its compounds are toxic when inhaled or injected into the bloodstream, though they are poorly absorbed following ingestion. The biological half-life of indium in humans is about two weeks.