How many moles of water are required to produce 4.5 moles of HNO3 according to the f.f reaction.

3NO2+H2O->2HNO3+NO

From the balanced chemical equation, we can see that for 2 moles of HNO3 produced, 1 mole of water is required.

So, for 4.5 moles of HNO3 produced, we need:

= (4.5 mol HNO3) x (1 mol H2O / 2 mol HNO3)
= 2.25 moles of water

Therefore, 2.25 moles of water are required to produce 4.5 moles of HNO3 according to the given reaction.