Explain, in terms of their bonding, how the presence of oxygen and ozone in the ozone layer helps to prevent both higher and lower energy UV light from reaching the surface of the Earth.

bonds in oxygen are double and bonds in ozone are (intermediate) between single and double;

bonds in oxygen are stronger / bonds in ozone are weaker;

oxygen absorbs higher energy UV light / ozone absorbs lower energy UV light;

Although part (a) was generally well answered, many candidates missed the first mark through failing to refer to bonds in both oxygen and ozone.