Some reactions of $NO_2$ relevant to photochemical smog formation are:
$NO_{2(g)} \xrightarrow{hv} NO_{(g)} + X$
$X + O_2 \rightarrow Y$
$NO + Y \rightarrow NO_2 + A$
$O + O_2 + M \rightarrow B + M$
Identify $A, B, X$ and $Y$.

• A
  $X = [O], Y = O_3, A = O_2, B = O_3$
• B
  $X = N_2O, Y = [O], A = O_3, B = NO$
• C
  $X = \frac{1}{2} O_2, Y = NO_2, A = O_3, B = O_2$
• D
  $X = NO, Y = [O], A = O_2, B = N_2O_3$