For the reaction 2NO + Br2 → 2NOBr, the following mechanism is given
\(\rm NO \ + \ Br_2 \ \overset{Fast}{\rightleftharpoons} \ NOBr_2 \)
\(\rm NOBr_2 \ + \ NO \ \xrightarrow{Slow} \ 2NOBr\)
Hence rate law is
1
k [NO]2[Br2]
2
k [NO][Br2]
3
k [NOBr2][NO]
4
k [NO] [Br2]2