The $pH$ of rainwater is generally about 5.6. This is due to the presence of dissolved carbon dioxide from the atmosphere that forms carbonic acid, a weak acid. This is a well-known natural phenomenon, often referred to as "acid rain" when pollution causes the $pH$ levels to drop further due to other acidic compounds.
Concept of $pH$:$pH$ is a scale used to specify the acidity or basicity of an aqueous solution. Pure water is neutral with a $pH$ of 7. Any $pH$ value less than 7 indicates acidic nature, while values greater than 7 indicate a basic nature.
Natural Rainwater $pH$: As rainwater falls through the atmosphere, it interacts with carbon dioxide forming carbonic acid, which slightly lowers its $pH$. This results in the natural rainwater having a $pH$ of approximately 5.6, making it slightly acidic.
Conclusion: Given the options, 5.6 is the closest approxi-mation to the natural $pH$ of rainwater, making it the correct answer. The other values provided are either neutral or more alkaline, which does not align with the typical $pH$ of rain.
Therefore, the correct answer to the question is 5.6.
