Confusion regarding order of reaction

The following points are given in my textbook about order and molecularity:-


(i) Order of a reaction is an experimental quantity. It can be zero and even a fraction but molecularity cannot be zero or a non-integer. Its values are limited to 1,2 or 3.


(ii) Order is applicable to elementary as well as complex reactions whereas molecularity is applicable only for elementary reactions.For a complex reaction, molecularity has no meaning.


(iii) Order is given by the slowest step(also known as RDS) and molecularity of the slowest step is same as the order of the overall reaction.


(iv) Molecularity is equal to the sum of stoichiometric coefficients of reactants in the elementary reaction.


However, I have observed an inconsistency in the above points and would like a clarification.


Let us consider 2 cases:-


****Case 1:** Complex Reaction**


By (iii)-order of overall reaction=molecularity of RDS. Since molecularity is 1,2 or 3, order must also be 1, 2 or 3.


**Case 2:Elementary Reaction**


By (iii)-order of overall reaction=molecularity of the reaction(since there is only 1 step so that must be the RDS). Since molecularity is 1,2 or 3, order must also be 1,2 or 3.


Now, combining these two cases, order =1,2 or 3. However, (i) mentions that the order can be fractional or zero. How is this possible?




Here is some clarification.


1. You are correct that order of reaction is an experimental quantity.
2. Just like order of reaction is is an experimental quantity, [molecularity](https://en.wikipedia.org/wiki/Molecularity) is purely theoretical quantity and as of today, I have not found anyone who can observe it. And, it only work for [elementary (1-step) reaction](https://en.wikipedia.org/wiki/Elementary_reaction).
3. Order of reactions do only measurable for RDS. But just by stating that there exist an RDS, you are also stating that the reaction is not elementary, thus the idea of molecularity simply does not apply for a reaction with more than one step.
4. Molecularity have to be positive whole number the same reason you cannot have less than one atom, it is simply not make sense.


I hope this clear things up.


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