# Is it possible to have Zero order Elementary Reaction?

I was going through a question, which got me confused. Is decomposition of NH3, an elementary reaction?

1. I have studied that for elementary reactions, Order = Molecularity, if so, then why they are different in this reaction.

2. If this is not an elementary reaction, Then molecularity has no significance. Each step should have its own molecularity. isn't it?

3. So, Is it possible to have zero order elementary reaction ? (Note also that the order of a reaction is measured experimentally as the sum of the powers to which reactants are raised in the rate expression, $rate= kA^aB^bC^c$ the order is $a+b+c$. Often it is the case that an apparently simple reaction such as $\ce{H2 + I2 }$ is only fully understood by a complex series of reactions, in this case the rate expression has fractional and reciprocal orders. The molecularity m refers to the coefficients in an elementary reaction, for example $m = a + b$ if the reaction actually occurs in a step $aA+bB \rightarrow$ so that m is a small positive number usually $1$ or $2$, for example $m=1;\, A\rightarrow product$ or $m=2;\, A+B\rightarrow product$)