How many moles of hydrogen are evolved when an excess of sodium metal is added to one mole of citric acid?

The formula of citric acid is:

CO2H

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HO - C - CH2CO2H

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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.