What kind of process is integrated organic farming?

Which of the following is incorrect?

How many sentences are correct?
$(1)$ $CNG$ burns most efficiently.
$(2)$ $CNG$ cannot be adulterated.
$(3)$ $CNG$ is cheaper than petrol and diesel.
$(4)$ In the $1990$s,Delhi ranked $4$th among the $41$ most polluted cities of the world.

Choose the incorrect statement.

The quantity of $CO_2$ in the atmosphere is about (in $\%$)

Estuaries occur in which of the following Indian states?