HL Paper 1
What is the major reason why the pH of unpolluted rain is less than 7?
A. methane
B. carbon dioxide
C. nitrogen oxides
D. sulfur dioxide
Markscheme
B
Examiners report
69 % of the candidates identified CO2 as the gas responsible for the acidity of unpolluted rain. The majority of the candidates that answered incorrectly chose nitrogen oxides (C) or sulfur dioxide (D).