How man Atoms in 1 bottle of coke?

Assuming that coke is mostly water, and the volume of the bottle is 0.3L:

The molecular mass of water is 18 g/mol, and there are 6.022x10^23 molecules in one mol. 0.3L pure water has the mass 300 g, which corresponds to 300/18 = 16.67 mol.

That corresponds to 16.67x6.022x10^23 = 1x10^25 molecules of water. As one molecule of water is made up from 3 atoms (one oxygen and two hydrogen), one bottle of coke would contain approximately 3x10^25 atoms.