For 2NO + O2 -> 2NO2 the mechanism is: fast equilibrium 2NO N2O2 (constant K), then slow N2O2 + O2 -> 2NO2 (constant k_2). The rate expressed in terms of reactants is

JEE Main levelSingle correct optionDifficulty 2 of 3ck192

For $2 NO + O X_{2} 2 NO X_{2}$ the mechanism is: fast equilibrium $2 NO N X_{2} O X_{2}$ (constant $K$ ), then slow $N X_{2} O X_{2} + O X_{2} 2 NO X_{2}$ (constant $k_{2}$ ). The rate expressed in terms of reactants is

The slow step gives rate

= k_{2} [N X_{2} O X_{2}] [O X_{2}]

. The intermediate is eliminated using the pre-equilibrium

[N X_{2} O X_{2}] = K [NO]^{2}

, giving rate

= k_{2} K [NO]^{2} [O X_{2}]