Which of the following statements is correct?
(1) Order of a reaction can be known from experimental results and not from the stoichiometry of a reaction.
(2) Molecularity of a reaction refers to (i) each of the elementary steps in (an overall mechanism of) a complex reaction or (ii) a single-step reaction.
(3) Overall molecularity of a reaction may be determined in a manner similar to the overall order of the reaction.
(4) Overall order of a reaction \(A^m + B^n \longrightarrow AB_x\) is m + n.
Select the correct answer using the following codes:

1,2 and 3

The correct answer is option 4. 1,2 and 3

(1) Order of a reaction can be known from experimental results and not from the stoichiometry of a reaction.

The order of a reaction is determined by experimental results, not by the stoichiometry of the reaction. This is because the order of a reaction is defined as the sum of the powers of the concentrations of the reactants in the rate equation, which is determined experimentally. Therefore, statement (1) is correct.

(2) Molecularity of a reaction refers to (i) each of the elementary steps in (an overall mechanism of) a complex reaction or (ii) a single-step reaction.

The molecularity of a reaction refers to the number of molecules involved in an elementary (single-step) reaction. It can refer to each of the elementary steps in a complex reaction or a single step reaction. Therefore, statement (2) is correct.

(3) Overall molecularity of a reaction may be determined in a manner similar to the overall order of the reaction.

This statement is partially correct. Determining the overall molecularity of a reaction is somewhat similar to determining the overall order of the reaction, but there are some key differences.

The overall molecularity of a reaction refers to the number of molecules (or ions, atoms, etc.) that must collide simultaneously in order for the reaction to occur. It is determined experimentally by studying the reaction mechanism and observing the dependence of the reaction rate on the concentrations of the reactants.

Similarly, the overall order of a reaction is determined experimentally by observing how changes in the concentrations of the reactants affect the rate of the reaction.

In both cases, the goal is to understand the relationship between the concentration of reactants and the rate of the reaction. However, the determination of overall molecularity typically involves a more detailed analysis of the reaction mechanism, whereas determining the overall order of the reaction focuses more on the empirical observation of how changes in concentration affect the rate.

In some cases, the overall molecularity of a reaction may match the overall order, particularly in simple elementary reactions where the reaction mechanism directly reflects the overall rate equation. However, this is not always the case, especially in more complex reaction mechanisms where the overall rate equation may not directly reflect the number of molecules involved in the rate-determining step.

Therefore, the correct answer is (4) 1, 2, and 3.

Let us see why statement 4 is false. The overall order of a reaction is not necessarily the sum of the stoichiometric coefficients of the reactants in the balanced equation. Instead, it is the sum of the individual reaction orders with respect to each reactant. These reaction orders can be determined experimentally and may not necessarily match the stoichiometric coefficients.

For example, the reaction \(A^m + B^n \longrightarrow AB_x\) could have an overall order that is different from \(m + n\) if the reaction rate is not solely determined by the concentrations of \(A\) and \(B\). Each reactant's concentration can have a different impact on the rate of the reaction, as determined by their respective reaction orders.