The right answer is 4 NH3 + 5 O2 --> 4 NO + 6 H2O.
In chemistry, an equation establishes what happened during a chemical reaction. On the left side of the equation, we place the reagents that were used for the experiment and on the right, the products obtained during the experiment. According to the principle of conservation of the mass (Lavoisier) during a chemical reaction, no atom disappears, none is created, they combine differently. In summary, you must have the same number of atoms of each element on the right as on the left of the equation. This is why a balance equation must always be balanced.
The simplest method is to balance an equation by the trial and error method.
