Which components are present in the stratosphere?

Identify the correct statements from the following:
$a$) $BOD$ value of clean water is less than $5 \ ppm$
$b$) Oxidation of ethene in the presence of $Pd^{2+}$ catalyst in aqueous medium gives acetic acid
$c$) Photochemical smog causes damage to plant life
$d$) Reducing smog is a mixture of smoke,fog and $SO_2$

Pure water would have a $BOD$ value of

Which one of the following is not a common component of photo-chemical smog?

In environmental chemistry,the medium which is affected by a pollutant is called the

Addition of phosphate fertilisers to water bodies causes