Gas A, found in the upper layers of the atmosphere, is a deadly poison but is essential for all living beings. The amount of this gas started declining sharply in the 1980s. Identify Gas A. How is it formed at higher levels of the atmosphere? Why is it essential for all living beings? State the cause for the depletion of this gas.

Gas A is Ozone. Alternatively, accept the formula of the gas. Ozone at the higher levels of the atmosphere is a product of UV radiation acting on oxygen (O2) molecule. The higher energy UV radiations split apart some molecular oxygen (O2) into free oxygen (O) atoms. These atoms then combine with molecular oxygen to form ozone. Alternatively, accept the following equations with the correct molecular formulae. No mark to be assigned if molecular formulae are not correct, when only the equation is written. Ozone shields the surface of the earth / protects living organisms from ultraviolet (UV) radiation released by the sun.Chlorofluorocarbons (CFCs) which are used as refrigerants / in fire extinguishers lead to depletion of ozone layer.

Gas A, found in the upper layers of the atmosphere, is a deadly poison but is essential for all living beings. The amount of this gas started declining sharply in the 1980s. - Science

Question

Gas A, found in the upper layers of the atmosphere, is a deadly poison but is essential for all living beings. The amount of this gas started declining sharply in the 1980s.

Identify Gas A. How is it formed at higher levels of the atmosphere?
Why is it essential for all living beings? State the cause for the depletion of this gas.

Answer in Brief

Solution

Gas A is Ozone. Alternatively, accept the formula of the gas. Ozone at the higher levels of the atmosphere is a product of UV radiation acting on oxygen (O₂) molecule. The higher energy UV radiations split apart some molecular oxygen (O₂) into free oxygen (O) atoms. These atoms then combine with molecular oxygen to form ozone.
Alternatively, accept the following equations with the correct molecular formulae. No mark to be assigned if molecular formulae are not correct, when only the equation is written.
Ozone shields the surface of the earth / protects living organisms from ultraviolet (UV) radiation released by the sun.
Chlorofluorocarbons (CFCs) which are used as refrigerants / in fire extinguishers lead to depletion of ozone layer.