Answer
26.5 kg
Work Step by Step
1 mole of $H_{2}$ can generate 2 mol of electrons.
Amount of electricity used by the house in a month = 850 kWh = 2.65 X $10^4$ mol of electrons.
MW of $H_{2}$ = 2
Amount of $H_{2}$ required = (2.65 X $10^4$) X (1/2) X (2) =26.5 kg
