One essential step in the manufacture of many plant fertilizers is the production of nitrogen monoxide

gas, NO (g). This step is represented by the following balanced equation:
4 NH (g) + 5 0 (g) › 4 NO (g) + 6 HO(1)
Determine the amount of oxygen needed to produce 1.2 x 104 mol of nitrogen monoxide gas.

first, the equation is not balanced.

4NH3 + 5O2 → 4NO + 6H2O
If this is right, then you will need 5/4 moles of O2 for every mole of NO. That gives 1.5*10^4 moles of O2