Which one of the following statements is $NOT$ correct?

Some statements are given:
$(S_1) \ CO_2$ is a greenhouse gas.
$(S_2)$ Classical smog contains smoke,fog,and a high concentration of $SO_2$.
$(S_3) \ DDT$ is biodegradable.
$(S_4)$ Drinking water should have a high $B.O.D.$
Which is the correct sequence of true $(T)$ or false $(F)$ regarding the above statements?

Reducing smog is a mixture of

Water pollution is caused due to

Among the gases $(a)-(e)$,the gases that cause greenhouse effect are
$(a) CO_2$; $(b) H_2O$; $(c) CFCs$; $(d) O_2$; $(e) O_3$

The concentration of dissolved oxygen in water for the growth of fish should be more than $X \ ppm$ and the Biochemical Oxygen Demand $(BOD)$ in clean water should be less than $Y \ ppm$. $X$ and $Y$ in $ppm$ are,respectively: