Which is the best definition of rate-determining step? an elementary step that often occurs in the reaction mechanism the elementary step that limits how fast the overall reaction proceeds an elementary step that is used to derive a rate law the unimolecular step in a reaction mechanism

The   elementary  step  that  limit  how  fast  the  overall   reaction  proceed  is the  best   definition of rate  determining  step

 Explanation

The   rate determining  step  is the slowest step of a chemical reaction that  determine  the speed at which the overall  reaction  proceeds.

for   example
elementary  step 1 ;  No2 + No2→NO  + NO3  ( slow)
elementary  step 2; No3 +  CO  → No2 +CO2  (fast)

The   elementary  step  1  is the   rate determining  step  since  it is   the slowest  step

The answer is c - the principal of original lateral continuity.