Use the reaction, which produces ammonia, to answer the question.

N2(g) + 3H2(g) ⇄ 2NH3(g)
Which change would happen in the system if the concentration of N2 was increased at constant pressure?

If the concentration of N2 is increased at constant pressure, according to Le Chatelier's principle, the system will respond by shifting the equilibrium in the reverse direction. This means that some of the N2 will react with H2 to form more NH3 until a new equilibrium is established. This will result in a decrease in the concentration of H2 and NH3.