What would happen if NO were added to N2(g) plus O2(g) 2NO(g) at equilibrium?

Answer 1

N2(g) + O2(g) <===>2NO(g)
Adding NO would push the reaction to the left, toward the reactants. This is according to Le Chatelier.

Answer 2

Adding NO would shift the equilibrium position to the left, favoring the formation of N2 and O2. This occurs to compensate for the increase in product concentration, restoring equilibrium. The concentrations of N2 and O2 would increase, while the concentration of NO would decrease.