Peroxy Acetyl Nitrate $(PAN)$,a class of hazardous air pollutants,stems from:
$I.$ $O_{2}$
$II.$ $SO_{x}$
$III.$ $NO_{x}$
$IV.$ $HC$

The chemical present in Flit is

Catalytic converters:
$I.$ These are fitted into automobiles for reducing emission of poisonous gases like $NO_x$ and $CO$.
$II.$ They have expensive metals like platinum,palladium,and rhodium as catalysts.
$III.$ As the exhaust emission passes through the catalytic converter,nitric oxide splits into nitrogen and oxygen; carbon monoxide is oxidized to carbon dioxide,and unburnt hydrocarbons are burnt completely into $CO_2$ and $H_2O$.
$IV.$ Motor vehicles fitted with catalytic converters should use unleaded petrol because lead in the petrol inactivates the catalyst.
Which of the statements given above are correct about catalytic converters?

Photochemical transformation of the automobile exhaust emission in $UV$ wavelength of sunlight results into

What does a high $BOD$ of water indicate?

What are the three major kinds of impurities in domestic wastewater?