Chemistry
Oxide of sulphur present in the atmosphere are washed down by rains to cause :

Eutrophication in lakes
Industrial smog formation
Depletion of fossil fuel reserves
Lowering of pH of soil

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Chemistry
Water is not effective in extinguishing a fire caused by petrol because

Water and petrol react chemically
Water and petrol are miscible with each other
Water and petrol are immiscible with each other and petrol which forms the upper layer continues to burn
The flame is too hot for water to cool it down

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