Discuss the following in brief:
$(a)$ Greenhouse gases
$(b)$ Catalytic converters
$(c)$ Ultraviolet-$B$ $(UV-B)$

(N/A) Greenhouse gases: Greenhouse gases are responsible for the greenhouse effect. They absorb infrared radiation from the earth and emit it again towards the earth,thus keeping the earth warm. Examples include $CO_2$,methane,and $CFCs$. Excessive emission of these gases leads to global warming and climate change.
$(b)$ Catalytic converters: These are fitted into automobiles to reduce the emission of poisonous gases. They contain expensive metals like platinum-palladium and rhodium as catalysts. As the exhaust passes through the catalytic converter,unburnt hydrocarbons are converted into $CO_2$ and water,and carbon monoxide and nitric oxide are changed to $CO_2$ and nitrogen gas,respectively.
$(c)$ Ultraviolet-$B$ $(UV-B)$: $UV-B$ radiation damages $DNA$ and causes mutations. It leads to skin aging,damage to skin cells,and various types of skin cancers. In human eyes,the cornea absorbs $UV-B$ radiation,and a high dose of $UV-B$ causes inflammation of the cornea,known as snow-blindness,cataract,etc. Such exposure may permanently damage the cornea.