How are aldehydes produced in the atmosphere?

Match List-$I$ with List-$II$.

List-$I$	List-$II$
$A$. Nitrogen oxides in air	$I$. Eutrophication
$B$. Methane in air	$II$. $pH$ of rain water becomes $5.6$
$C$. Carbon dioxide	$III$. Global warming
$D$. Phosphate fertilisers in water	$IV$. Acid rain

Choose the correct answer from the options given below:

Biochemical Oxygen Demand,$(BOD)$ is a measure of organic material present in water. $BOD$ value less than $5 \ ppm$ indicates a water sample to be ..... .

Which of the following statements about smog is/are correct?
$(i)$ Smog formed on sunny days contains oxidizing molecules.
$(ii)$ Photochemical smog contains many reactive molecules.
$(iii)$ The main polluting components of smog are oxides of carbon.
$(iv)$ The presence of carbon monoxide in air leads to the formation of ozone in smog.

Name the acids present in acid rain and state their sources in rainwater.

Biosphere refers to