Anu showed Appu a sample of water from the Ganga River. It was not transparent and contained some suspended grime. Appu said that he could make it drinkable. He filtered the water using a filter paper to remove the grime. The filtered water was clean; Appu also boiled this water to kill harmful microbes and gave it to Anu to drink. Anu said that the water was still polluted and undrinkable. Can you say why?

The water contained dissolved chemicals

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The water contained harmful microbes

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The water contained undissolved impurities

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None of the above

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Solution

The correct option is A
The water contained dissolved chemicals

Undissolved impurities in water can be removed by filtration. Microbes can be killed by boiling. However, dissolved harmful chemicals such as pesticides, fertilisers, mercury and lead salts cannot be removed by any of the above methods. These impurities are not visible and do not change the colour of water. Thus, they can make water unfit for drinking.

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