Which of the following is least biodegradable?

The greenhouse gas(es) is/are:
$A$. Carbon dioxide
$B$. Oxygen
$C$. Water vapour
$D$. Methane
Choose the most appropriate answer from the options given below:

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

The depletion of ozone in Antarctica is caused by the formation of which of the following substances?

Classical smog occurs in which of the following atmospheres?

Which of the following chemicals is not involved in photochemical smog formation?