10 most difficult elements riddles

Iron is most abundant in the Earth's outer and inner core, and it is the fourth most common element in the Earth's crust.

Radioactive nickel-56 (which decays to the most common isotope of iron) is the last element to be produced before the collapse of a supernova. That is why the iron was abundantly scattered into space after the supernova explosion.

Bismuth metal has been known since ancient times, although it was often confused with lead and tin, which share some physical properties. The etymology is uncertain, but possibly comes from Arabic bi ismid, meaning having the properties of antimony or the German words weiße Masse or Wismuth ("white mass"), translated in the mid-sixteenth century to New Latin bisemutum.

A nutrient is a component in foods that is used by an organism to survive and grow. Macronutrients are broken down and converted into the energy needed by an organism's metabolic system to function. Micronutrients provide the necessary cofactors for metabolism to be carried out; they are also used to build and repair tissues and regulate body processes.

Depleted uranium is 1.67 times as dense as lead, 84% as dense as osmium or iridium, which are the densest known substances under standard (i.e., Earth-surface) pressures. Consequently a depleted uranium projectile of given mass has a smaller diameter than an equivalent lead projectile, with less aerodynamic drag and deeper (armor-piercing) penetration due to a higher pressure at point of impact.

Many of technetium's properties were predicted by Dmitri Mendeleev, who left a gap in his periodic table before the element was discovered. It was finally discovered by Emilio Segrè and Carlo Perrier in 1937 and named after the Greek word τεχνητός, meaning "artificial", since it was the first element to be artificially produced.

Iridium was discovered in 1803 among insoluble impurities in natural platinum. Smithson Tennant, the primary discoverer, named iridium for the Greek goddess Iris, personification of the rainbow, because of the striking and diverse colors of its salts. Iridium is one of the rarest elements in Earth's crust, with annual production and consumption of only three tonnes.

Three isotopes of hydrogen occur naturally on the Earth: the most frequent protium (1H), deuterium (2H) and tritium (3H). Other isotopes of hydrogen (4H-7H) were created in laboratories and are highly unstable.

When large deposit of graphite was found in the 16th century in England, it was thought to be a form of lead. In many languages, the word for pencil literally means lead pen. (German Bleistift, Polish ołówek, Arabic قلم رصاص)

Helium was first discovered in 1868 as the unexpected line in the spectrum of the chromosphere of the Sun - and so it was named after the Greek word Helios (Sun).