Cyanosis is caused by

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?

According to the Central Pollution Control Board $(CPCB)$,what size (in diameter) of particulate matter is responsible for causing the greatest harm to human health?

Compare the lifestyle of people living in urban areas with those in rural areas and briefly describe how the lifestyle affects their health.

Which one of the following is an environment-related disorder with the correct main cause?

Some toxic substances present in industrial waste water can undergo $.........$ in the aquatic food chain.