Which of the following acts as a secondary pollutant?

In agriculture,improper drainage of water leads to:
$I-$ The soil becomes waterlogged.
$II -$ The soil surface draws up salts from the water.
$III -$ Salts are deposited as a thin crust on the land surface.
$IV -$ Salts start accumulating around the roots of the plants.
$V -$ The increasing concentration of salts becomes favorable for crop growth.
$VI -$ It is highly beneficial for agriculture.
Which of the above statements are correct?

What is used to reduce the emission of poisonous gases from vehicles?

$...............$ is any undesirable change in the physical,chemical,or biological characteristics of air,land,water,or soil.

Spraying of pesticide is an example of

According to the Euro $III$ norms,what was the controlled limit for sulfur content in petrol?