Which of the following is responsible for a sound level of $150 \, dB$ or more?

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

Catalytic converters,which have expensive metals as catalysts,are fitted into automobiles for reducing emission of poisonous gases. Which of the following is $NOT$ used in them?

Air pollutants:
$I.$ Cause injury to all living organisms.
$II.$ Reduce growth and yield of crops and cause premature death of plants.
$III.$ Affect the respiratory system of humans and animals.
Which of the statements given above are correct?

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.

$A$ chemical that acts as a pollutant in the troposphere but as a protectant in the stratosphere is: