The formula of citric acid is:
CO2H
|
HO - C - CH2CO2H
|
C - CH2 CO2H
I bolded the 4 hydrogens that can be subsituted by sodium.
Three of those hydrogens belong to carboxyl group (- CO2H) and one to a hydroxyl group (- OH).
You need to take into account that 4 H will form 2 H2 molecules.
So, the answer is that 2 moles of molecules will be formed from 1 mole of citric acid molecules.
