Explanation
The correct answer is (a) 1872.
The term "acid rain" was first used in 1872 by Scottish chemist Robert Angus Smith. In his book "Air and Rain: The Beginnings of a Chemical Climatology," Smith described the phenomenon of acidic precipitation resulting from the industrial emissions of sulfur dioxide and nitrogen oxides.
Smith observed the damaging effects of acidic rain on vegetation and buildings in industrialized areas, particularly in Manchester, England. His research and observations laid the foundation for the understanding of acid rain as a global environmental issue caused by human activities.
Therefore, the correct answer is (a) 1872.
