Given the balanced equation representing a reaction: 4nh3 (g) + 5o2 (g) → 4no(g) + 6h2o(g) what is the number of moles of h2o(g) formed when 2.0 moles of nh3 (g) react completely?

To solve, you find the correct mole ratio from the given equation. The questions asks for how many moles of H2O from 2.0 moles of NH3(ammonia), so the mole ration is going to be 6:4.
6 moles of  H2O and 4 moles of NH3.

Tip:
We multiply the given with what we want divided by what we want to get rid of.

So, 2.0mol NH3 x 6mol H2O /4mol NH3.

The answer is  3 moles of H2O or 3mol H2O

What are the options? i can you if you give them.