Calculate the atomic mass (average atomic mass) of naturally occurring oxygen.

Atomic mass is, literally, a measure of mass. 

One atomic mass unit is a very, very, very, very, very, very small fraction of a gram.

It is actually defined using the most common isotope of carbon, which is carbon-12.  

The average atomic mass of Oxygen is 15.999 u. 

This is what i found on google “when one phosphate group is removed by breaking a phosphoanhydride bond in a process called hydrolysis, energy is released, and atp is converted to adenosine diphosphate (adp). likewise, energy is also released when a phosphate is removed from adp to form adenosine monophosphate (amp).” i hope this you .