What is the reagent used for testing fluoride ion in water?

Photochemical smog consists of an excessive amount of $X$ in addition to aldehydes,ketones,$PAN$,etc. $X$ is:

$BOD$ values (in $ppm$) for clean water $(A)$ and polluted water $(B)$ are expected respectively:

If water pollution continues at its present rate,it will eventually

How is the depletion of the ozone layer created in the atmosphere over Antarctica? Explain with reactions.

Acrolein $(X)$ is one of the chemicals formed when $O_3$ and $NO_2$ react with unburnt hydrocarbons present in the polluted air. The structure of '$X$' is