Quote from Miss.LeoRN
I learned early on in school that fighting questions never really helps. If you're struggling to the point where the one or two points you might get from a question "saves" you then you've got other issues to figure out rather than argue questions[...]
I learned this from reading posts on AN while I was in pre-nursing, and it holds true in my year and a half of experience. I think a big part of it is that these questions are not like math problems that are strictly formulaic. With nursing the questions are perception and judgement based, and students come at the question from different background experiences that can affect perception of the question. I feel the same way about these tests as you do, but we can only learn the info as best we can and utilize test-taking strategies (search these boards).
Since we don't have the full question, could the answer have been something like assess airway for clearance before administering O2? Administering O2 can be tricky with things like COPD, but 51 is significantly lower than I think would be ok for an advanced case of COPD.
*just reread the OP. Yep, that looks like one of those questions where one book says start with NC, and another source says go right to 100% non-rebreather. I.e., I just took an ATI exam that states a 22ga IV cath is too small to use for blood products while my Lewis Med-Surg book states 22ga and larger is acceptable for blood (clinically I've seen 20ga and larger for blood). I wish there was an international standard for these kind of things...