Hello. Sorry by the late. Ok. I was wrong, I doesn't take care that details
. Ok. We got this redox:
2 H2O ---- 2 H+ + O2 + 4e-
The Faraday's definition consist that a Faraday (unit of charge) es equal to the charge of ONE MOLE of electrons. In this reaction we can see that four electrons by 2 molecules of Water there are in the change, or there are four electrons by one molecule of Oxygen. So, for one mole of Oxygen, we got four moles of electrons, or, wich is the same, 4 F (four Faraday's). The problem says that 1/2 mole of Oxygen was obtained (in STP), and ask for the charge requeride. Make your own conclusions.
P.D.: Isn't beautifull, the chemistry ?
P.P.D.: Sorry by my bad english.