Answer: Option (a) is the correct answer.
Step-by-step explanation:
When rain passes through the air then carbon dioxide present in the air dissolves in the water. Further, this carbon dioxide reacts with water and results in the formation of carbonic acid.
Thus, the rain water becomes acidic in nature and as a result, there will be decrease in its pH.
Hence, we can conclude that rain has a natural pH that is acidic.