To convert the atomic mass of an oxygen atom from atomic mass units (u) to kilograms (kg), you need to use the following conversion factor:
1 u = 1.66053906660 x 10^(-27) kg
Therefore, to convert 16.0 u to kilograms, you can use the conversion factor as follows:
16.0 u * (1.66053906660 x 10^(-27) kg/u) = 2.65686250656 x 10^(-26) kg
So, an atom of oxygen with an atomic mass of 16.0 u is approximately equal to 2.65686250656 x 10^(-26) kilograms.