The rarest naturally occurring element is astatine (At), with an estimate of only 25 grams in the earths crust. The rarest man-made element is francium, which has a half life of only 20 minutes, and must be constantly produced in order to be studied.
You are probably thinking of carbon dioxide (CO2) which is found is relatively small amounts in air, at least compared to nitrogen and oxygen, but there aren't compounds as they contain only a single element.
Xenon is a chemical element with the atomic number 54 and the symbol Xe. It is a colorless, odorless noble gas found in trace amounts in Earth's atmosphere.
Neither. Krypton is an element with the symbol Kr and atomic number 36. The name means "hidden one". It is found in trace amounts in the atmosphere.
In the case of each chemical element the name is found.
The element name "Xenon" comes from the Greek word "xenos", meaning "strange" or "foreign". Xenon is a colorless and odorless gas that is found in trace amounts in Earth's atmosphere.
Serous fluid is the name for several different kinds of watery liquids in the body. It is found in saliva, it drains from wounds in small amounts, and is found in mucus.
The element was discovered by (insert name of scientist or researcher).
oxygen
Copernicium is a synthetic element with the atomic number 112 and the symbol Cn. It was named in honor of the astronomer Nicolaus Copernicus. Copernicium is a highly radioactive element that has only been produced in small amounts in laboratories.
A colorless element that is one of the six inert gasses; occurs in trace amounts in air
The element with a valence electron configuration of 4s²4p⁴ is selenium (Se). It is located in group 16 of the periodic table and is known for its various allotropes and applications in electronics and glassmaking. Selenium is a nonmetal and is essential in small amounts for certain biological functions.
The gas found in stars is primarily hydrogen, with smaller amounts of helium and trace elements. These gases undergo nuclear fusion reactions to produce energy that powers the star's brightness and heat.