The electrostatic precipitator can remove over . . . . . . particulate matter. (in $;\%$)

Pick out the correct statement.

What does the term 'eutrophic lakes' mean?

Catalytic converters,which have expensive metals as catalysts,are fitted into automobiles for reducing emission of poisonous gases. Which of the following is $NOT$ used in them?

The natural aging of a lake by nutrient enrichment of its water is known as $..........$

In a polluted lake,the index of pollution is