Question

Why don't equal masses of carbon atoms and oxygen molecules contain the same number of particles?

Answer 1

It is because the calculations are made considering the number of moles rather than masses. Equal moles of any element contains equal number of particles.

2 mole of Carbon atoms contains the equal number of particles as 2 moles of oxygen. But 16 gm Carbon does not contain the equal number of particles as 16 gm oxygen as the number of moles in 16 gm carbon is not equal to number of moles in 16 gm oxygen.