Answer
A mechanism is considered plausible when each of the elementary steps when added together give the overall balanced equation and the it agrees with the experimentally determined rate law.
The term "plausible" mechanism is typically used instead of "correct" mechanism because there typically is no one mechanism that all reactants will follow the whole way through, as reactions can be somewhat random.
Most reaction mechanisms are a multi-step process.
Work Step by Step
Definitions provided in textbook.
