1. The problem statement, all variables and given/known data Ammonia and sulfur dioxide are reducing agents. Acidified potassium dichromate can be used to test for reducing agents. But sulfur dioxide can turn potassium dichromate from orange to green but ammonia cannot. Why? 2. The attempt at a solution From what I know, potassium dichromate is an oxidising agent, thus when it meets with ammonia and sulfur dioxide, it will turn from orange to green. However, ammonia cannot. I just need some rough idea on why because I'm still studying chemistry according to the syllabus in the British GCE O level. Thanks.