How many moles of oxygen gas can be produced during electrolytic decomposition of 180 g of water?

$\underset{2\mathrm{x}18=36\mathrm{g}}{2{\mathrm{H}}_2\mathrm{O}}\to 2{\mathrm{H}}_2+{\mathrm{O}}_2$
36 g of water produces 1 mole of O₂ gas.
180 g of water will produce $\frac{180}{36}$ = 5 moles of O₂ gas.