Question

How can we identify zero order reaction?

Answer 1

The only theoretical way of firmly establishing the order of a reaction (if it has one) is to fully calculate its kinetic law (or rate equation), which can only be done if you know the scheme of the reaction, i.e. the list of all elementary reactions involved.

There is one case where you can take a shortcut, namely if you know (or strongly suspect) that the reaction in question is an elementary reaction, for example, if it involves no catalyst, proceeds in a single step with only one transition state and no intermediate. If that is the case, then the order of the reaction is determined by the stoichiometry (A⟶XA⟶X is first order, 2A⟶X2A⟶X or A+B⟶XA+B⟶X are second order)