As a subject matter expert in the field of chemistry and physics, I can provide you with an informed answer regarding the rarity of krypton.

Krypton is a chemical element with the symbol Kr and atomic number 36. It is a member of the noble gases, which are characterized by their low reactivity due to having a full complement of valence electrons. Krypton is indeed considered to be a rare gas. In the Earth's atmosphere, krypton is present at very low concentrations, approximately 1 part per million (ppm). This makes it one of the less abundant noble gases in the atmosphere. However, when compared to other elements in the Earth's crust, krypton is not particularly rare. It is more abundant than some elements like gold, silver, or platinum.

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Krypton is a colorless, odorless, tasteless gas. It is one of the so-called inert gases found in Group 18 of the periodic table. It is a rare gas present in air at a concentration of about one part per million. Naturally occurring krypton is a mixture of six stable isotopes.read more >>