| Date | May 2015 | Marks available | 1 | Reference code | 15M.1.sl.TZ1.21 |
| Level | SL | Paper | 1 | Time zone | TZ1 |
| Command term | Question number | 21 | Adapted from | N/A |
Question
Which gas in the atmosphere causes the pH of unpolluted rain to be approximately 6?
A. Carbon dioxide
B. Sulfur dioxide
C. Oxygen
D. Nitrogen
Markscheme
A
Examiners report
Students found this question to be difficult with 38.16% correct answers; about 28% of students chose either C (oxygen) or D (nitrogen). Presence of \({\text{C}}{{\text{O}}_{\text{2}}}\) in the air causes pH of unpolluted rain water to be approximately 6 in many parts of the world.
