Thanks @DumbHollywoodActor for the very helpful answer. It is hence the order of the quantities of the gases that is the crux of the argument. The gold/silver/bronze medal analogy is great.
The gold standard of tutors is probably @"Jonathan Wang" . He's far more expensive than the others, but if you can afford it, it could be a good investment.
Thanks for another great session today everyone! A take away from today: a gold standard in BR is to take the wrong answer choice that you had trouble with and change it to say what it should have said to be the right answer choice.