Euro-$II$ emission norms were introduced for reducing which of the following?

In $1984$,the Bhopal gas tragedy was caused due to the leakage of

Nitrogen oxides are produced from the emissions of automobiles and power stations,which are a source of fine particulate matter in the air,leading to the formation of .....

Which among the following is likely to have the highest levels of $D.D.T.$ depositions in its body?

Assertion: $A$ suspended particulate matter $(SPM)$ is an important pollutant released by diesel vehicles.
Reason: Catalytic converters greatly reduce pollution caused by automobiles.

$A$ dental disease characterized by mottling of teeth is due to the presence of a certain chemical element in drinking water. Which is that element?