The cause of water bloom is ..........

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?

Particulate matter with a diameter of $2.5$ micrometres or less and a sound level of $150$ $dB$ or more causes the greatest harm to human health.

The Taj Mahal is threatened due to the effect of:

According to the $..........$ norms,the implementation of $.......$ vehicles was enforced across the country from $1^{st}$ April $2017$.

What is $B.O.D$?