Hoffmans apparatus

find out the energy available per mole of water if it is split into h2 and o2

Data 1 mol of gas at NTP is 24.5l
31.2ml of _______
62.4ml of _______

it looks like this question comes from a lab experiment. You have not provided all the details needed. Were you supposed to perform an experiemnt?

Your provided data only tells me how much H2O you separated with Hoffman's apparatus. Since the reaction is H2O-> H2 + (1/2) O2, you ended up with 62.4 ml of H2 and consumed 62.4 ml of H2O. That means you electrolyzed 62.4*10^-3/24.5 = 2.547*10^-3 moles or 0.0459 g of H2O.

The apparatus consumes electrical energy when doing the separation. Measuring that energy electrically will tell you the Gibbs free energy per mole.