Keen observation of the rates of reaction about the series of steps leading to the formation of products is called the reaction mechanism . The reaction between `H_(2)` and `I_(2)` to form hydrogen iodide was originally postulated as a simple one step reaction `H_(2) + I_(2) to 2 HI` Rate = `k [H_(2)][I_(2)]` but the formation of HI has been explained on the basis of the following mechanism `({:( I_(2) , to , 2 I "(fast)" , ... (i) ), ( H_(2) + I , to , H_(2) I "(fast)" , ... (ii)) , (H_(2) I + I , to , 2HI "(slow)" , ... (iii) ):})/("overall" H_(2) + I_(2) to 2 HI` For the reaction `2NO_(2) + F_(2) to 2 NO_(2) F` following mechanism has been provided `NO_(2) + F_(2) overset("slow")(to) NO_(2)F + F` `NO_(2) + F overset("fast")(to) NO_(2)F` Thus rate expression of the above reaction can be written asA. `r = k[NO_(2)]^(2) [F_(2)]`B. `r = k[NO_(2)]`C. `r = k [NO_(2)][F_(2)]`D. `r = k [F_(2)]`