What does a 100% atom economy mean?

A 100% atom economy signifies that all the atoms present in the reactants are fully utilized and transformed into valuable products. This concept is essential in assessing the efficiency and sustainability of chemical reactions. When a reaction exhibits a 100% atom economy, it means that there are no unreacted materials remaining, and every atom contributes to the final useful product. This outcome is highly desirable in green chemistry as it minimizes waste and enhances the overall efficiency of the process.

While it may seem that some of the other options touch upon aspects of atom economy, they do not capture its full meaning. Option A incorrectly suggests that all atoms are wasted, which contradicts the principle of 100% atom economy. Option C notes the absence of by-products, which could be true in many contexts of high atom economy but does not encompass the complete definition. Similarly, option D speaks generally about the production of waste materials but does not explicitly highlight the relationship with the conversion of reactants into useful products. Hence, the characteristic that defines a perfect atom economy is centered on the full conversion of all reactant atoms into products, making the selected answer correct.