$BOD$ stands for

The gaseous envelope around the earth is known as the atmosphere. The lowest layer of this extends up to $10 \ km$ from sea level; this layer is $.......$

Polar stratospheric clouds facilitate the formation of .... .

Explain the damage to the troposphere caused by $CO$ and $CO_2$.

Which of the following is a renewable resource?

$A$ large number of fish are suddenly found floating dead on a lake. There is no evidence of toxic dumping,but you find an abundance of phytoplankton. Suggest a reason for the fish kill.