Faraday S Law

The reduction half-reaction for in acid medium is given by: This equation shows that for each mole of , 6 moles of electrons are required for the reduction. Thus, for 3.5 moles of , the total number of moles of electrons required will be: Since 1 Faraday corresponds to 1 mole of electrons, the total charge required in Faraday units will be 21 Faradays.
Thus, the correct answer is 21.0 Faradays.