Identify the coldest region among the following layers of atmosphere.

Which of the following gases causes the depletion of the ozone layer in the upper atmosphere?

The term 'Biosphere' refers to:

Which of the following statements are correct?
$A$. Ocean is a sink for $CO_2$.
$B$. Greenhouse effect causes lowering of the temperature of the earth's surface.
$C$. To control $CO$ emission by automobiles,usually catalytic converters are fitted into exhaust pipes.
$D$. $H_2SO_4$,herbicides,and insecticides form mist.

In drinking water,if the maximum prescribed concentration of copper is $x \ mg \ dm^{-3}$,the maximum prescribed concentration of zinc will be

Which substance is now used in refrigerators instead of $CFC$s?