Which from following formulae is a correct formula to determine percent atom economy?

• A

  $\%$ Atom economy $=$ Formula weight of product $\times 100$
• B

  $\%$ Atom economy $=$ Sum of formula weight of all reactant $\times 100$
• Correct answer
  C

  $\%$ Atom economy $=\frac{\text { Formula weight of desired product }}{\text { Sum of formula weight of allreactant }} \times 100$
• D

  $\%$ Atom economy $=\frac{\text { Sum of formula weight of all reactant }}{\text { Formula weight of desired product }} \times 100$

Hence, the correct answer is option: 'C'.