Final answer:
The equilibrium expression for the reaction 2NO (g) ⇌ N₂ (g) + O₂ (g) is K = [N₂][O₂]/[NO]^2.
Step-by-step explanation:
The correct equilibrium expression for the given reversible reaction, 2NO (g) ⇌ N₂ (g) + O₂ (g), is based on the law of mass action which states that the rate of a chemical reaction at equilibrium is proportional to the product of the concentrations of the reactants each raised to the power of their respective coefficients in the balanced equation.
To write this equilibrium expression, we identify the products and the reactants and their coefficients. For the reactants, we have 2NO, and for the products, we have N₂ and O₂, each with a coefficient of 1.
The equilibrium constant expression, K, for this reaction is therefore:
K = \frac{[N₂][O₂]}{[NO]^2}
Where [N₂], [O₂], and [NO] represent the molar concentrations of nitrogen gas, oxygen gas, and nitrogen monoxide gas, respectively.