Formation of photochemical smog involves the following reaction in which $$\mathrm{A}, \mathrm{B}$$ and $$\mathrm{C}$$ are respectively.

$$ \begin{aligned} & \text { i. } \mathrm{NO}_{2} \stackrel{\mathrm{h} v}{\longrightarrow} \mathrm{A}+\mathrm{B} \\ & \text { ii. } \mathrm{B}+\mathrm{O}_{2} \rightarrow \mathrm{C} \\ & \text { iii. } \mathrm{A}+\mathrm{C} \rightarrow \mathrm{NO}_{2}+\mathrm{O}_{2} \end{aligned} $$

Choose the correct answer from the options given below :

The concentration of dissolved Oxygen in water for growth of fish should be more than $$\mathrm{\underline X }$$ ppm and Biochemical Oxygen Demand in clean water should be less than $$\mathrm{\underline Y }$$ ppm. X and Y in ppm are, respectively.

Correct statement about smog is :

Some reactions of NO$$_2$$ relevant to photochemical smog formation are

Identify A, B, X and Y :