Assertion (A): Rainwater usually has a pH of 5.6.

Reason (R): This is due to the presence of $H 2 S O 4$ and $H N O 3$ and produced from oxides of sulphur and nitrogen.

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Both A and R are true and R is the correct explanation of A.

Both A and R are true but R is not the correct explanation of A.

A is true, and R is false.

A is false and R is true.

answer is C.

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Detailed Solution

Concept: Due to the presence of air gases in the troposphere, rainwater is naturally acidified. These gases naturally contribute to the acidity of rainfall, but human activity increases their concentration through the combustion of fossil fuels, leading to unnaturally acidic precipitation.
While unpolluted, natural rainwater has a pH of 5.5 to 5.6, fresh, pure water has a pH of 7. As a result, rainwater that is natural and untainted is acidic.
Carbon dioxide, nitrogen, and other gases make up the majority of this gas mixture. The abundance of

, and

in the troposphere is what causes unpolluted precipitation to be acidic.
It becomes acidic when carbon dioxide and water combine to generate carbonic acid, which then dissociates to release hydrogen ions. Nitric oxide, a product of the interaction between oxygen and nitrogen in the air after lightning, also adds to the acidity of precipitation. Rainwater becomes acidic when NO in the atmosphere is converted to nitrogen dioxide, which then combines with water to produce nitric acid.
The majority of the acidity in natural rainfall is caused by carbon dioxide, as we can see from the explanation above, hence the reason is false.
Hence, the correct answer is option 3.

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