The least prevalent gas in the atmosphere was oxygen several billion years ago. This is because it was only around 2.4-3 billion years ago when the first photosynthetic bacteria evolved, meaning they produce food from inorganic compounds such as carbon dioxide and water to produce glucose and oxygen. Oxygen is then released in the atmosphere and this is called <em>The Great Oxygenation Event</em>.
False. Alkaline earth metals react with oxygen.
A3B2
bond is ionic
A is in group 2 (you can pick any like Ca)
B is in group 5 (like B)
the other question:
the reason is they are neutral gas and they already have 8 electrons except for He which is 2 and are completely stable so don't want to loose any electron vs Li and Na which have only 1 electron in the outer layer and are willing to loose that one to become stable.
