Impurities of water are

In big cities,the major atmospheric pollutant is

What does '$X$' represent in the given figure?

Release of phosphates and nitrates in water bodies ($i.e.$,in rivers and lakes) leads to:

Non-ionising radiations damaging to $DNA$ are

Which measures can be taken to control noise pollution?
$I-$ Use of sound-absorbent materials or mufflers in industries.
$II-$ Creating horn-free zones around hospitals and schools.
$III-$ Setting permissible sound levels for firecrackers and loud speakers.
$IV-$ Restricting the use of loudspeakers after a certain time.