The correct answer is option 'B': Only a and b.

Depletion of the ozone layer is primarily caused by the release of certain chemicals called ozone-depleting substances (ODS), such as chlorofluorocarbons (CFCs), halons, and carbon tetrachloride. These substances are released into the atmosphere through various human activities, including industrial processes, aerosol propellants, and the use of certain chemicals.

Depletion of the ozone layer has several harmful effects on the environment and human health. The two effects mentioned in the answer options are:

a) Cataract in eyes leading to blindness:
Exposure to high levels of ultraviolet (UV) radiation due to ozone depletion can lead to the development of cataracts in the eyes. UV radiation can damage the proteins in the lens of the eye, leading to clouding and loss of transparency. Over time, this can cause vision impairment and, in severe cases, blindness.

b) Reduced productivity of forests:
Ozone depletion can also have adverse effects on ecosystems, including forests. High levels of UV radiation can inhibit the growth and productivity of plants, including trees in forests. UV radiation can damage plant cells, impair photosynthesis, and reduce the overall health and productivity of forest ecosystems. This can lead to reduced timber production, decreased biodiversity, and disruption of ecological balance.

c) Lung infection:
While lung infection is not directly caused by ozone depletion, it is worth noting that depletion of the ozone layer can indirectly contribute to the increase in respiratory diseases. UV radiation can weaken the immune system, making individuals more susceptible to various infections, including respiratory infections. Additionally, ozone depletion can alter weather patterns and increase air pollution, which can further worsen respiratory health.

In conclusion, depletion of the ozone layer has various harmful effects, including cataract formation in eyes leading to blindness and reduced productivity of forests. It is crucial to take measures to reduce the release of ozone-depleting substances and protect the ozone layer to prevent these adverse consequences.