Green muffler is used against which type of pollution?

Which steps were taken in Delhi to reduce pollution from vehicles?
$I-$ Phasing out of old vehicles
$II -$ Use of leaded petrol
$III -$ Use of low-sulphur petrol and diesel
$IV -$ Use of catalytic converters in vehicles
$V -$ Application of stringent pollution level norms for vehicles

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 smog formed in congested metropolitan cities mainly consists of

The Bhopal gas tragedy in $1984$ was caused by the leakage of which gas?

Which of the following is a photochemical reaction product?