Is krypton a rare element?
krypton is a noble gas, and it's found in the atomosphere. Most of air is nitrogen, and then oxygen (about 70% 21% respectively). That means that of all the rest of the possible gases that can be part of the air, all together they make up 9%. Krypton is part of that. "rare" is a very qualitative measure. I am sure there is more krypton than other gases, but not as much as others. krypton can be purchased by chemistry departments, and it does not cost thousands of dollars, so again, it's there even though it's not as abundant as oxygen.
There are two elements that derive their names from Greek words meaning hidden: Krypton and Lanthanum. Krypton is from the Greek root word for hidden, krypto. The element krypton is a noble gas often used in fluorescent lamps. Lanthanum is from another Greek term meaning hidden, lanthanein. It's called that because it is very difficult to separate from the other rare earth elements. It is a silvery white metallic element with many uses.