Answer: the calculation of the number of atoms conserved in the desired product rather than in waste.
Step-by-step explanation:
Atom economy gives how much desired product is obtained compared to amount of starting materials.
![\text {Atom economy}=\frac{\text {molecular weight of desired product}}{\text {molecular weight of all products}}* 100%](https://img.qammunity.org/2021/formulas/chemistry/high-school/z1h91qznbked8fes559659byszinn02ra9.png)
For example:
![CH_4+2O_2\rightarrow CO_2+2H_2O](https://img.qammunity.org/2021/formulas/chemistry/middle-school/onsvykmg46lpdg5eg5qnw040tkvck96tuw.png)
![\text {atom economy of water}=\frac{\text {molecular weight of desired product}}{\text {molecular weight of all products}}* 100%](https://img.qammunity.org/2021/formulas/chemistry/high-school/4an270s6ji6o4v7dqzjaqdrcfi3r40bq65.png)
![\text {atom economy of water}=(36)/(44+36)* 100%=45\%](https://img.qammunity.org/2021/formulas/chemistry/high-school/7uy36hi9i0go2qno2i8dxi0ax4g7mitomi.png)
Thus atom economy for water is 45%