If the reaction 2NO + 2H2 --> N2 + 2H2O occurred in just a single step, the overall order of the reaction would be

A) 1
B) 2
C) 3
D) 4
E) 5

The overall order of a reaction can be determined by adding up the individual orders of the reactants involved in the rate equation. In this case, the rate equation would be:

rate = k[NO]^a[H2]^b

where a and b are the respective orders of NO and H2.

According to the balanced equation 2NO + 2H2 -> N2 + 2H2O, it can be observed that the coefficients of NO and H2 are both 2.

If the reaction were to occur in a single step, it would imply that the reaction rate is directly proportional to the concentration of each reactant raised to the power of their corresponding coefficients:

rate = k[NO]^2[H2]^2

Thus, the overall order of the reaction would be the sum of the exponents, which is 2 + 2 = 4.

Therefore, the correct answer is D) 4.

To determine the overall order of the reaction, we need to know the molecularity of the reaction. The molecularity of a reaction refers to the number of molecules that must come together to react in a single step.

In this case, the given reaction 2NO + 2H2 → N2 + 2H2O involves two NO molecules and two H2 molecules reacting in a single step. Therefore, the molecularity of this reaction is 4.

The overall order of a reaction is the sum of the individual reactant orders. Since each reactant has an order of 1 (because they are both raised to the power of 1 in the balanced equation), the overall order of the reaction is equal to the sum of the individual reactant orders. In this case, the overall order of the reaction would be:

Overall Order = Order of NO + Order of H2
Overall Order = 1 + 1
Overall Order = 2

Therefore, the answer is B) 2.