Water pollution is caused due to

Given below are two statements :
Statement $I$ : If $BOD$ is $4\,ppm$ and dissolved oxygen is $8\,ppm$,then it is a good quality water.
Statement $II$ : If the concentration of zinc and nitrate salts are $5\,ppm$ each,then it can be a good quality water.
In the light of the above statements,choose the most appropriate answer from the options given below :

What is environmental pollution?

The $BOD$ values for pure water and highly polluted water are respectively

Match List-$I$ with List-$II$ :

List-$I$ (Species)	List-$II$ (Maximum allowed concentration in ppm in drinking water)
$A$. $F^{-}$	$I$. $< 50 \, ppm$
$B$. $SO_{4}^{2-}$	$II$. $< 5 \, ppm$
$C$. $NO_{3}^{-}$	$III$. $< 2 \, ppm$
$D$. $Zn$	$IV$. $< 500 \, ppm$

Given below are two statements:
Statement $I:$ Classical smog occurs in cool humid climate. It is a reducing mixture of smoke,fog and sulphur dioxide.
Statement $II:$ Photochemical smog has components,ozone,nitric oxide,acrolein,formaldehyde,$PAN$ etc.
In the light of above statements,choose the most appropriate answer from the options given below: