To solve this question we need to use the reaction equation proportion.
The reaction is: 2 H2O -> 2 H2 + O2
The equation tells us that 2 moles of H2O produce 2 moles of H2 and 1 mole of O2.
So, if 2 moles of H2O produce 1 mole of O2
0.5 moles of H2O produce x mole of O2
Here we can do a rule of 3:
2 moles of H2O --- 1 mole of O2
0.5 moles of H2O --- x mole of O2
0.5 x 1 = 2x
x = 0.5/2
x = 0.25 mole
Answer: The number of moles of O2 produced is 0.25 moles.