The balanced chemical equation for above question is-

NaClO3 + H2O -> NaClO4 + H2

The oxidation state of Cl atom in NaClO3 is +5 and the oxidation state of Cl atom in NaClO4 is +7. So, the net change in oxidation state = 7-5 = +2.

This show that 2 faradays of charge is required to get 1 mole of NaClO4.

So if 1 faradays of charge is  passed through NaclO3  then (1/2) mole of NaClO4 obtained.

Then 3 faradays of charge is  passed through NaclO3  then (1/2)x3 mole of NaClO4 obtained that is 1.5 mole NaClO4 is obtained.