Question

in the atmosphere,oxygen is available as O2 but not as O

Answer 1

yes because it does not occur as free state in nature

Answer 2

It does exist as O just not for very long as it will promptly react with just about anything it comes into contact with which can give up or share an electron with it. Including electron donor atoms bound to any electron acceptor which is less able to hold onto electrons than Oxygen, the only electron acceptor that can hold electrons more strongly than Oxygen is Fluorine so it will quickly oxidise just about anything that can possibly become oxidised.another reason cam be Oxygen by itself doesn't have enough electrons to be stable so it shares electrons with another oxygen atom. This creates diatomic oxygen molecules, each one consisting of two oxygen atoms sharing electrons with one another. Since this is the most common form of oxygen, its formula is written as "O2" rather than just "O".