Which of the following causes the depletion of the ozone layer in the stratosphere?

$NO_2$ and $O_3$ react with unburnt hydrocarbons in polluted air to form .....

Rain water is considered as acid rain if its $pH$ is less than.......

$A$ water sample is reported to be highly polluted if the $BOD$ (Biological Oxygen Demand) value of the sample becomes:

Identify the reactions that occur in photochemical smog.
$(i)$ $CH_2=O + H_2 \longrightarrow CH_3OH$
$(ii)$ $NO_{2(g)} \xrightarrow{h \nu} NO_{(g)} + O_{(g)}$; $O_{(g)} + O_{2(g)} \longrightarrow O_{3(g)}$
$(iii)$ $CH_4 + 2O_3 \longrightarrow CH_2=O + 2H_2O$
$(iv)$ $NO_{(g)} + O_{3(g)} \longrightarrow NO_{2(g)} + O_{2(g)}$

Carbon monoxide gas is more dangerous than carbon dioxide gas. Why?