Reaction between `NO_2` and `CO` to give `CO_2` and NO takes place by the following mechanism:
Write the rate expression and order of the reaction. What is the unit of rate constant ?

Explanation

`NO_2+NO_2overset("Slow")(rarr)NO+NO_3`
`NO_3+CO overset("Fast")(rarr)NO_2+CO_2`
In a multistep reaction, the slowest step is the rate determining step. Therefore, the rate of the complete reaction will depend upon the first step i.e
`NO_2+NO_2overset("Slow")(rarr)NO+NO_3`
`therefore` rate=`k[NO_2][NO_2]=k[NO_2]^2`
Order=2