Question

Assertion (A) : The amount of ozone in the atmosphere began to drop sharply in the 1980s. Reason (R) : The oxygen atoms combine with molecular oxygen to form ozone.

A gas 'X' which is a deadly poison is found at the higher levels of atmosphere and performs an essential function. Name the gas and write the function performed by this gas in the atmosphere. Which chemical is linked to the decrease in the level of this gas? What measures have been taken by an international organization to check the depletion of the layer containing this gas?