Which of the following metals is a water pollutant and causes sterility in human beings?

Why is $CNG$ considered a better fuel than diesel/petrol?
$I.$ $CNG$ burns most efficiently without leaving any unburnt remnant behind.
$II.$ $CNG$ is cheaper than petrol or diesel.
$III.$ $CNG$ cannot be siphoned off by thieves and adulterated like petrol or diesel.
Which of the statements given above are correct?

The higher the $BOD$ of waste water,the higher is the amount of .......... in it.

Cotton pollen grains are an important pollutant in which of the following cities?

$SO_{2}$ pollution affects

Pesticides disturb the ecosystem by eliminating the