The most hazardous metal pollutant of automobile exhaust is

What is causing concern for the Taj Mahal?

What happens when nitrates and phosphates are added to a lake?

Compressed Natural Gas $(CNG)$ is primarily composed of:

Which one of the following is the heavy toxic metal present in waste water from industries?

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.