Use atomic masses H 1, C 12, O 16, Na 23, Cl 35.5, Br 80. Which of the following reactions has the lowest atom economy for the organic product named first?

Atom economy is the mass of desired product divided by the total mass of reactants. Values: addition of hydrogen $28+2$ giving $30$ is 100%; dehydration $28/46$ is 60.87%; chlorination $50.5/87$ is 58.05%; substitution of bromide $46/(109+40)=46/149$ is 30.87%, the lowest.